Lysophospholipid Receptors (Signaling and Biochemistry) || Sphingosine 1-Phosphate (S1P) Signaling...

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CHAPTER 14

Sphingosine 1-Phosphate (S1P) Signaling in Cardiovascular Physiology and DiseaseBODO LEVKAU

14.1. SPHINGOSINE 1-PHOSPHATE (S1P) IN PLASMA: SOURCES AND CARRIERS

Plasma concentrations of S1P are between 200 and 1000 nM (1, 2). Its major sources in plasma are hematopoietic cells. Of those, erythrocytes are quanti-tatively the most important ones. They lack S1P lyase, an important S1P degrading enzyme, and are enormously potent in synthesizing S1P from sphin-gosine and subsequently in releasing it. Platelets, mast cells, and leukocytes, especially upon activation, can also produce and secrete S1P. In addition, vas-cular endothelial cells have also been shown to synthesize and release S1P, while S1P production by lymphatic endothelial cells is both necessary and sufficient for the maintenance of the S1P content of the lymph (3, 4).

Inside the cell, S1P moves freely between membranes but requires specific transport mechanisms for its translocation to the outer leaflet of the cytoplas-mic membrane (5, 6). Only from there can it be released into the microenvi-ronment in general and in plasma in particular. The involved transport mechanisms for the majority of cell types are still unknown. In some cells such as platelets and mast cells, ATP-binding cassette (ABC)-type transporters have been implicated in the export of S1P (7, 8), while in erythrocytes, a yet unidentified ABC transporter without requirement for ATP hydrolysis has been suggested (9). However, plasma S1P levels are unaltered in mice deficient for ABCA1, ABCA7, or ABCC1 (10), suggesting that they are dispensable for the maintenance of plasma S1P levels. Recently, a designated sphingolipid transporter named spinster homologue 2 (Spns2, cause of the two of hearts

Lysophospholipid Receptors: Signaling and Biochemistry, First Edition. Edited by Jerold Chun, Timothy Hla, Sara Spiegel, and Wouter Moolenaar.© 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc.

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mutation) has been identified in zebrafish (11, 12), but its relevance for plasma S1P is yet unknown.

While the cellular sources of plasma S1P are well known, the release of S1P from cells does not occur without a biochemical acceptor being present in plasma as the amphipathic nature of S1P does not allow its presence in a free, unbound form in plasma. There, S1P is bound mainly to lipoproteins, of which high-density lipoproteins (HDLs) are the most important carriers for S1P (∼60–90%), followed by albumin (∼10–20%) and other lipoproteins such as low-density lipoproteins (LDLs) and very low-density lipoproteins (VLDLs) (together less than 10%) (13, 14). Remarkably, S1P binds with an extremely high affinity to HDL, making these lipoproteins the primary biochemical acceptors for plasma S1P (15). Accordingly, plasma S1P levels positively cor-relate with HDL-cholesterol (HDL-C) levels as well as the levels of the two major apolipoproteins within HDL—apolipoproteins AI and AII (2). The way S1P is transferred from cells to HDL is unknown—both a passive transfer from erythrocyte membranes to the HDL particle (16) and a transport via a yet unidentified erythrocyte ABC transporter (see above) (9) have been pro-posed. In both cases, a direct contact between HDL and the erythrocyte has been postulated as being necessary.

Another intriguing issue is the nature of the HDL constituent(s) that are able to “extract” S1P from cells and keep it bound to the HDL particle. While several apolipoproteins may have the biophysical properties of binding S1P, one in particular, apolipoprotein M (ApoM), has been found to bind S1P in vitro (17), but most importantly, to do so in vivo (18). Mice deficient for ApoM had lower plasma S1P levels and their HDL almost completely lacked S1P (18). Interestingly, ApoM-deficient HDL had also less biological activity that is usually attributed to the S1P content of HDL, such as the ability to activate Akt and Erks, promote endothelial cell migration, and induce formation of endothelial adherens junctions (18).

As stated above, concentrations of S1P in plasma range between 200 and 1000 nM (1, 2). Remarkably, this is roughly 20- to 100-fold higher than the Kd value of its receptors (13, 19). Nevertheless, the biologically active fraction of the total plasma S1P content is only 1–2% (13), suggesting that the largest part of S1P is inaccessible for signaling purposes. While the biological sense of such excess is not easily revealed, the much smaller but biologically active part of plasma S1P may offer important clues. If we were to focus on its major carrier in plasma (HDL), there is vast evidence that HDL is by no means a buffer or neutralizer of S1P. It appears to be actually the opposite: S1P presented to cells and organs in an HDL-associated form is biologically active. Several of the well-known biological effects of HDL can partially or even entirely be attributed to the biological actions of the S1P content of HDL (14). These are, among others, NO-dependent vasodilatation, angiogenesis, Akt and Erk sig-naling, as well as certain aspects of the antioxidative, antiapoptotic, and anti-inflammatory actions of HDL (14). How much of the S1P contained in HDL is actually biologically active (e.g., able to gain access to S1P receptors and

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exert signaling) is not known. What is known is that the capacity of HDL to take up exogenous S1P is enormous (up to 10-fold more per milligram of protein than the amount that it normally carries). Nevertheless, the biochemi-cal packaging, topography, and presentation of S1P cargo that HDL carries outside of the HDL particle for the purpose of biological action are still under investigation. In summary, plasma is the extracellular compartment with the highest S1P levels, but its bioavailability and signaling propensity are deter-mined in a crucial way by its most important plasma carrier: HDL.

14.2. S1P PRODUCING AND DEGRADING ENZYMES IN THE HEART AND THE VASCULATURE

Sphingosine kinases 1 and 2 (Sphk1 and Sphk2) are both expressed and enzy-matically active in the adult rodent heart (20). Their cardiac expression has been found as early as embryonic day (E) E8.5 (21). Interestingly, Sphk2 activ-ity, but not that of Sphk1, decreases in the aging heart (22). S1P phosphatase 1 (SPP1) is also expressed in the adult heart of mice and men (23, 24) and throughout the early stages of cardiac development (21). The gene for S1P lyase (Sgpl1) is transcriptionally active in the rodent heart (25), the protein is expressed, and the enzyme is active (26). S1P lyase is specifically expressed in cardiomyocytes and has a much lower expression, or no expression at all, in cardiac fibroblasts (26). In the vasculature, Sphk1 is present in arteries, but its expression differs dependent on the vascular bed: for example, the mRNA is expressed 40- to 80-fold higher in cerebral arteries than in the aorta or mesenteric arteries (27). The mRNA encoding SPP1 has been shown to be expressed in Hamster gracilis muscle resistance arteries (28).

14.3. S1P RECEPTORS IN THE HEART AND VESSEL WALL

There are five cognate G protein-coupled receptors, S1P1–5, to which S1P spe-cifically binds with a Kd of 8–20 nM (29). The details on receptor binding and activation are complex as individual S1P receptors can couple to one or more G proteins with considerable overlap: Of the main cardiovascular S1P recep-tors, S1P1 is coupled to Gi/o (preferentially Giα1 and Giα3); S1P2 to Gi/o, G12/13, and Gq; and S1P3 to either Gi/o, Gq, or G12/13 (5, 29).

The coupling of one receptor to different G proteins, and the simultaneous activation of several S1P receptors by their ligand, explains the many down-stream signaling pathways elicited by S1P (30). Classical examples of vertical, nonredundant S1P signaling are the activation of phospholipase C (PLC) and the Ca2+ mobilization via Gq, the activation of Erks and PI3-kinase, as well as the inhibition of adenylate cyclase via Gi, and the activation of Rho/actin cytoskeleton assembly via G12/13. In addition, S1P receptors have been shown to transactivate tyrosine kinase receptors such as those for vascular endothelial


growth factor (VEGF), platelet-derived growth factor (PDGF), and epidermal growth factor (EGF) (31–34), as well as other G protein-coupled receptors such as the CXCR4 (35–37). A cross activation of the TGF-β receptor type II by an activation of Smads has also been described (38). S1P receptor signaling occurs at the full spectrum of the receptor occupancy curve: Low concentra-tions lead to the transactivation of the PDGF receptor; those at the steep slope of the curve turn off lymphocyte recirculation, while high concentrations (50- to 100-fold higher than the Kd) lead to receptor desensitization and degrada-tion (39).

The S1P receptors predominantly expressed in the adult rodent heart are S1P1, S1P2, and S1P3 with S1P1 being approximately four- to sixfold more abundant than the other two receptors (40). Adult human hearts express similar amounts of S1P1 and S1P3 and much less S1P2. S1P1 is strongly expressed in ventricular, septal, and atrial cardiomyocytes and in the endothelial cells of cardiac vessels (41). S1P receptors S1P1–3 are expressed from E8.5 to E12.5 in the developing mouse heart together with S1P4, a receptor otherwise almost exclusively expressed in lymphoid tissue (21).

Endothelial cells express predominantly S1P1, less S1P3, and only little S1P2 under normal circumstances (42–44). However, S1P2 becomes crucially impor-tant in endothelial pathologies such as hypoxic retinopathy (45). Furthermore, endothelial cells of different origins (arteries, capillaries, veins, lymphatics) and those from different arteries (aortic, cerebral, coronary, renal, and mesenteric) have apparently different relative amounts of S1P receptors (46, 47), although this has not been systematically studied.

Vascular smooth muscle cells (VSMCs) express mainly S1P2, less S1P3 and even less S1P1 (43). Again, different arteries have different expression levels of S1P receptors, which has been proposed as an explanation for the different extent of S1P-mediated vasoconstriction in the aorta versus cerebral arteries (48) (see below). In addition, pup-intimal VSMCs express higher levels of S1P1 than adult-medial VSMCs (49) and respond differently to S1P, which may underlie certain vascular pathologies (see below).

14.4. S1P SIGNALING IN CARDIAC DEVELOPMENT

S1P signaling has been shown to have an impact on heart development in zebrafish because the miles apart (mil) mutation—an orthologue to the mam-manlian S1P2—results in impaired fusion of the bilateral heart tubes leading to cardia bifida (50). Interestingly, its expression is required in extracardiac tissue and not in the precardiac cells that normally migrate to the midline and fuse to the definitive heart tube (50). This indicates that S1P signaling is involved in early cardiac morphogenesis. However, S1P signaling is important during early heart development as well. It influences the migration, differentia-tion, and survival of embryonic cardiac cells (21). It appears that the mainte-nance of a specific concentration range of S1P is necessary specifically for

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cardiac cushion development. Both a decrease and an increase in S1P concen-trations hamper the development of atrioventricular (AV) canal cushions, with an S1P decrease leading to cell death and an S1P increase reduces cell migra-tion and inhibits mesenchymal cell formation (21).

S1P2 and S1P3 knockout mice have an apparently normal embryogenesis with no overt cardiac phenotype (51–53). Knockout mice for S1P1 die during embryogenesis between E12.5 and E14.5 due to the hemorrhage caused by vascular defects (see below), which has hampered investigation of S1P1 in cardiac development and adult heart function. To overcome this, we have generated cardiomyocyte-restricted S1P1-deficient mice, in which no overt heart defects are present at birth, but a heart failure phenotype develops throughout life (see below).

14.5. S1P IN VASCULAR MORPHOGENESIS

S1P1 knockout mice die during embryogenesis between E12.5 and E14.5 due to hemorrhage because of the inability of VSMCs to surround and support the developing vasculature (52). The recruitment of VSMC requires S1P1 in endothelial cells, but not VSMC, suggesting that paracrine effects play an important role, especially as endothelial-specific S1P1 knockout mice exhibit the same lethal, hemorrhage-caused phenotype as the global S1P1 knockout mice (54). This looks strongly like the paracrine effect of the mil mutation in the zebrafish heart (50). Identical defects are displayed by mice lacking S1P due to a genetic deletion of both of the S1P-synthesizing enzymes Sphk1 and Sphk2 (55). This clearly demonstrates the causal role of S1P in vascular mor-phogenesis during development. Several S1P effects studied in vitro may offer clues to the nature of the in vivo defects on vascular maturation and morpho-genesis: S1P stimulates endothelial proliferation, migration, and angiogenesis, protects endothelial cells against apoptosis, and controls vascular permeability (56, 57). It is also a potent chemoattractant for endothelial cells (58) and promotes directed migration, vascular differentiation, and formation of capil-lary networks on complex extracellular matrices (52, 59). Small GTPases play an important role in mediating these effects of S1P: Rac1 activation by S1P1 signaling induces focal contact assembly, membrane ruffling, and cortical actin formation via Gi, while RhoA activation by S1P3 promotes stress fiber assem-bly via Gq.

S1P2 and S1P3 play discrete roles in vascular development, which are not evident in single receptor knockout mice, but are revealed by additional vas-cular defects in the S1P1, S1P2, and S1P3 triple null embryos; these die earlier (between E10.5 and E11.5) than the S1P1 knockout alone, and they also exhibit a more severe phenotype (60). S1P2 signaling appears to have both antimigra-tory and antiangiogenic effects: Pharmacological S1P2 blockade enhances the promigratory response of S1P elicited by S1P1 in endothelial cells, while overexpression of S1P2 inhibits S1P-induced migration by suppressing Rac1


activity (61). S1P2 has been shown to be a hypoxia-regulated gene, and its deletion in mice makes them resistant to the pathological neoangiogenesis triggered by hypoxia, suggesting that S1P2 is a causal factor in ischemia-driven retinopathy (62). Vice versa, S1P2 activation by S1P leads to hypoxia-independent activation of hypoxia-inducible factor 1 (HIF-1) and transcrip-tional activation of HIF-1-regulated genes such as VEGF (63). Tumor-associated angiogenesis is another S1P-responsive process: An antibody that neutralizes bioactive S1P in vivo has been shown to reduce tumor angiogenesis and block tumor progression in several xenograft and allograft tumor models (64). In vivo, the same antibody in a humanized version inhibited retinal and choroidal neovascularization in a model of oxygen-induced ischemic retinopathy (65).

14.6. S1P IN MYOCARDIAL REPERFUSION INJURY AND PRECONDITIONING: S1P RECEPTORS, SPHINGOSINE KINASES, AND S1P LYASE

Reduced S1P synthesis and impaired S1P signaling causally contribute to myocardial tissue injury following ischemia and ischemia/reperfusion, respec-tively, of the heart—the two pathologies underlying any myocardial damage occurring after coronary artery occlusion in humans. S1P and Sphks are causal players in the myocardial self-protection mechanisms against ischemia/reperfusion injury, as well as in the processes of ischemic pre- and postcondi-tioning (66). In isolated mouse hearts subjected to ischemia/reperfusion, exog-enous administration of S1P improved hemodynamics, reduced creatinine kinase release, and diminished infarct size (67)—clear evidence for a beneficial effect on myocardial tissue. This is also the case in vivo, where administration of S1P prior to transient ischemia/reperfusion substantially reduced infarct size in a mouse model of acute myocardial infarction (AMI) (68). These data have suggested that S1P generation by endogenous Sphk may play a major role in cardioprotection. Indeed, a decline of Sphk enzyme activity accompa-nied by a decrease of S1P levels has been described to occur during ischemia in the heart, and the hearts of mice deficient for Sphk1 have larger infarct sizes when subjected to ischemia/reperfusion injury (69). In agreement, the hearts of heterozygous S1P lyase knockout mice exhibited smaller infarct sizes and an increased functional recovery after ischemia/reperfusion (26). An inhibitor of the S1P lyase—the Food and Drug Administration (FDA)-approved food additive tetrahydroxybutylimidazole (THI)—also reduced infarct size and enhanced hemodynamic recovery (26).

S1P and Sphks are also involved in ischemic preconditioning (67), a process where brief periods of ischemia activate endogenous mechanisms that render the heart resistant to damage caused by subsequent prolonged periods of isch-emia and reperfusion. Ischemic preconditioning is associated with an increase in cardiac S1P levels and prevents the decline of Sphk enzyme activity during ischemia (70). Pharmacological inhibition of Sphk by dimethylsphingosine

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(DMS) abolishes the benefit of ischemic preconditioning (71), and precondi-tioning is absent in hearts from SphK1-deficient mice (72). In contrast, adeno-viral gene transfer of Sphk1 protects against myocardial damage and the hemodynamic deterioration occurring during acute ischemia/reperfusion injury in isolated rat hearts (73). Just recently, not only Sphk1 but also Sphk2 was demonstrated to protect against ischemia/reperfusion injury and to con-tribute to ischemic preconditioning: Cardiac damage was larger and ischemic preconditioning absent, respectively, in hearts of Sphk2-deficient mice (74). However, the mechanisms of cardioprotection by Sphk1 and Sphk2 are appar-ently quite different (see below).

The mechanisms involved in ischemic preconditioning are extremely complex, but they all converge to inhibit the mitochondrial permeability tran-sition pore (mPTP), the critical determinant of lethal reperfusion injury (75). S1P participates in several aspects of preconditioning. The cytokine TNFα is involved in the endogenous protection exhibited by ischemic preconditioning (76) and is known to activate both sphingomyelinase and Sphk activities (77–81). Thus, Sphk may be a mediator of the beneficial TNFα effect in pre-conditioning, especially in inhibition of ceramidase—the enzyme that cata-lyzes the conversion of ceramide to sphingosine—by N-oleoylethanolamine (NOE) abolishes both ischemic and TNFα-mediated preconditioning (71, 76). The anesthetic isoflurane, a well-known preconditioning agent in many organs including the heart (82), protects the kidney against ischemia/reperfusion injury via Sphk activation and S1P production (83). Sphk activation appears to require intact εPKC signaling for ischemic preconditioning—an enzyme indispensable for ischemic preconditioning (84) because the beneficial effect of Sphk-activating agents such as the monoganglioside GM-1 are absent and the activating effect of preconditioning on Sphk1 is lost, respectively, in εPKC-deficient mice (66, 70, 85). However, exogenously administered S1P is effective in isolated εPKC-null hearts subjected to ischemia/reperfusion injury, suggest-ing that exogenous S1P is sufficient for protection (85). Indeed, exogenously administered S1P overrides the deleterious consequences of Sphk inhibition or Sphk deficiency on both infarct size and preconditioning (66, 70). Finally, S1P and Sphk1 are important not only in ischemic preconditioning but also in postconditioning in a similar manner (86). Postconditioning is a phenomenon where brief periods of ischemia/reperfusion are administered at the beginning of the reperfusion period following prolonged ischemia and act in a cardio-protective manner (87).

In contrast, Sphk2 has recently been suggested to utilize a different molecu-lar pathway than Sphk1 to achieve ischemic preconditioning and cardioprotec-tion (74). While the simplest explanation for the lack of preconditioning in Sphk2-deficient mice may be the need of Sphk2 besides Sphk1 for the main-tenance of a threshold S1P concentration required for preconditioning, another explanation has been proposed as well. Sphk2 has recently been shown to mediate S1P synthesis in the mitochondria, and this S1P pool appears to be important for the proper assembly of the respiratory chain (88). Sphk2-deficient


mice have decreased mitochondrial cytochrome oxidase activity and reduced respiration, which leads to increased reactive oxygen species (ROS) generation and may thus facilitate the opening of the mPTP and increase reperfusion injury.

If exogenous S1P can mediate cardioprotection, then its receptors should be the most obvious candidates to transmit the protective signal. However, the identity of the S1P receptors that mediate the preconditioning effect of S1P is currently unknown. All studies so far have concentrated on the role of S1P receptors in ischemia/reperfusion injury. Initial studies have concentrated on the prosurvival signaling of S1P receptors in isolated cardiomyocytes in vitro. Indeed, S1P rescues cardiomyocytes from hypoxia in a manner involving S1P1 and Gi-dependent activation of the survival kinase Akt as shown with the S1P1 receptor agonist SEW2871 (89, 90). A different study has implied S1P2 together with S1P3, but not S1P1, in Akt and Erk activation in cardiomyocytes, while S1P1 was found to be solely responsible for the decrease of cyclic adenosine monophosphate (cAMP) accumulation (91). In vivo evidence for the role of S1P receptors in cardioprotection has come from studies on myocardial infarc-tion in S1P receptor-deficient mice. Coronary ischemia/reperfusion injury was similar to wild-type mice in either S1P2-deficient or S1P3-deficient mice but was greatly enhanced (more than 50%) in double knockouts. Akt activation by ischemia/reperfusion and exogenous S1P was abolished in double-knockout hearts and isolated double-knockout cardiomyocytes, respectively (92).

A different study has confirmed an unaltered infarct size in S1P3 knockout mice (68). Exogenous application of S1P 30 minutes prior to ischemia/reperfusion in the same model of AMI, as described for the double-knockout mice above, substantially attenuated infarct size (68). This effect was dependent on the S1P3 receptor and its generation of nitric oxide (NO) since it was com-pletely abolished in S1P3-deficient mice, as well as through pharmacological NO synthase (NOS) inhibition (68). In this setting, the attenuation of infarct size by S1P was accompanied by a reduced inflammatory polymorphonuclear neutrophil recruitment to the infarction area and a decrease in cardiomyocyte apoptosis. Since cardioprotection can be ascribed to S1P-mediated NO genera-tion in this model, the protective effect S1P has on the endothelium may be more important than that on cardiomyocytes in this scenario. In fact, several endothelial S1P effects that are known to be beneficial in the setting of ischemia/reperfusion are known to be mediated by NO: endothelial cell barrier sealing, inhibition of polymorphonuclear neutrophil adhesion, and prevention of microvascular leakage (93, 94). Thus, increased NO production in the micro-circulation through engagement of endothelial S1P3 plays a crucial role. In contrast, the direct survival effects of S1P on cardiomyocytes described above may become increasingly important when, instead of the rather mild, inflammation-dominated injury caused by short ischemia/reperfusion, a more severe and cardiomyocyte death-dominated reperfusion damage occurs with increasingly longer ischemia periods. In this case, the direct and potent anti-apoptotic effects of S1P in cardiomyocytes, as shown both for isolated cells (68,

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95) and Langendorff perfused hearts (where no postischemic inflammation is present) (70), will predominate and join forces with the milder endothelial effects. In fact, there is evidence from a model of permanent coronary occlusion that impaired S1P signaling plays a role in the development of ischemic car-diomyopathy (96). There, Sphk activity was reduced and S1P1 receptor gene expression was decreased, respectively, early after infarction in the remote, uninfarcted myocardium. Interestingly, S1P1 activation with oral SEW2871 during the first 2 weeks after infarction resulted in improved myocardial func-tion (96). However, caution should be exercised with agonists such as SEW2871 as it induced irreversible tachyarrhythmias in the reperfusion period in one case (97). FTY720 also induced ventricular tachyarrhythmias and increased mortality when administered before reperfusion, but protected against reper-fusion arrhythmias when administered 24 hours prior to ischemia (98). The underlying mechanisms remain unclear. When FTY720 was administered in isolated rat hearts during reperfusion, it attenuated the rise in left ventricular end-diastolic pressure (LVEDP) and improved the recovery of left ventricular developed pressure (LVDP), but did not ameliorate infarct size; SEW2871 was not able to improve recovery and even increased LVDP (90). In vivo, FTY720 also did not alter infarct size—neither when given immediately at reperfusion nor 24 hours before (98).

The pathological remodeling that occurs in the left ventricle after myocar-dial infarction is the cause for cardiac dilation and ischemic cardiomyopathy, and cardiac fibroblasts are an important player in this process. Their transfor-mation into myofibroblasts and deposition of extracellular matrix are crucial determinants of pathological cardiac remodeling. Interestingly, Sphk activity is more than 10-fold higher in cardiac fibroblasts than in adult mouse cardio-myocytes; in cardiac fibroblasts, it promotes hypoxia-induced proliferation but dampens proinflammatory responses (99). In addition, S1P promotes myofi-broblast transformation and collagen expression in vitro in an S1P2-dependent manner, while the profibrotic cytokine TGF-β was able to activate Sphk1 (100). Interestingly, administration of an S1P-neutralizing antibody in a mouse coronary ligation model attenuated macrophage and mast cell infiltration into the infracted zone and reduced perivascular fibrosis within the noninfarcted myocardium, suggesting that S1P promotes pathological fibrosis (101). The effect of S1P blockade on cardiac function and remodeling after myocardial infarction in vivo still remains to be addressed.

14.7. CONTROL OF ARTERIAL TONE AND TISSUE PERFUSION BY S1P

S1P has been shown to play an important role in the regulation of arterial tone (46, 47). From the outside, it does so via S1P receptors on both endothelial and VSMCs through different signaling cascades, and in concert with other vasoac-tive substances. From the inside, S1P effects on the contractile mechanisms of


the smooth muscle cell have been proposed. Thus, both S1P receptor-dependent and -independent mechanisms are involved, and different S1P receptors play a role in different arteries. When applied exogenously to isolated vessels in tension myograph studies, S1P promotes vasoconstriction in mesenteric, cere-bral, and coronary arteries but is much less efficient in femoral and carotid arteries and the aorta. This effect has been suggested to occur via direct actions on VSMCs (47, 102). Different arteries appear to have different relative expres-sion levels of S1P receptors, which has been proposed as an explanation for the different potency of S1P-mediated vasoconstriction in aorta and cerebral arteries (48).

Basal vasoreactivity in response to S1P has been studied in different arter-ies of S1P receptor knockout mice. S1P-induced vasoconstriction in the basilar artery of wild-type and S1P2 deficient mice, but not in those of S1P3 deficient mice (102). Accordingly, phospho-FTY720 induced S1P3-mediated vasocon-striction in isolated cerebral arteries (102), which has been confirmed by studies using an S1P3 antagonist (103). This implies S1P3 as an important mediator of cerebral vasoconstriction. In vivo, coronary arteries also respond to S1P by decreasing myocardial perfusion by ∼25% without any effects on blood pressure in a completely S1P3-dependent manner (104).

In contrast, S1P2-deficient mice have a decreased resting vascular tone, as well as contractile responsiveness to α-adrenergic stimulation, which results in elevated regional blood flow and decreased mesenteric and renal resistance (but normal blood pressure) (105). The arteries’ contractile response to phen-ylephrin is blunted both in vivo and in isolated artery strips, suggesting that S1P2 regulates homeostatic arterial tone in the mesenterium and kidney (105). In fact, S1P produced and secreted by VSMC that engages the S1P2 receptor in a autocrine/paracrine manner is important for the myogenic response of resistance arteries—the unique intrinsic ability of an artery to constrict in response to increased transmural pressure caused by changes in systemic blood pressure in order to keep blood flow to the tissues constant (28, 106). The myogenic response involves a pool of extracellular S1P generated by Sphk and degraded by the intracellular enzyme SPP1; for degradation, S1P is imported into the cell by the cystic fibrosis transmembrane conductance regu-lator (CFTR), also known as ATP-binding cassette subfamily C member 7 [ABCC7]) (28).

However, the S1P receptor-independent effects of S1P in vascular tone control have been described as well, particularly via its role as an intracellular second messenger (102). Sphk1 can be stimulated by agonists of various G protein-coupled receptors, suggesting that S1P also acts as a second messenger for vasoconstrictors such as 5-hydroxytryptamine (5-HT) and even S1P itself (102). This occurs through an activation of Ca2+-sensitizing mechanisms such as the RhoA/Rho kinase pathway leading to increased myosin light-chain phosphorylation and contraction. Accordingly, Sphk inhibition and arteries from Sphk1 knockout mice have blunted vasoconstriction responses both to agonists and KCl. This is independent of S1P receptors as the contraction to

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the prostanoid U46619 and endothelin-1 (ET-1) in basilar arteries from S1P2 and S1P3 knockout mice did not differ from wild-type arteries (102), while Sphk inhibition by DMS blocked vasoconstriction in cerebral arteries from S1P3 knockout mice (27). These studies suggest that the effects of intracellular S1P generated by Sphk1 are important in the vasoconstriction induced by agonists of various G protein-coupled receptors. It should be noted in this context that not only S1P receptors are differently expressed in different arter-ies but so is Sphk1: It is expressed 40- to 80-fold higher in cerebral arteries than in the aorta or the mesenteric arteries (27).

Besides its effects on VSMC, S1P is an important stimulator of NO produc-tion in endothelial cells through its activation of the endothelial NOS (47, 107, 108). This has physiological consequences as S1P has been shown to dilate precontracted aortas of mice and rats ex vivo (102, 109) and reverse the endothelin-induced elevation of mean arterial pressure after intra-aortic injec-tion in vivo (109). Thus, S1P effects on endothelial cells counteract those on VSMC especially when arterial tone is already elevated, taking part in the intricate fine-tuning of vascular tone by S1P (46).

14.8. EFFECTS ON CARDIAC FUNCTION UNDER NORMAL AND PATHOLOGICAL HEMODYNAMIC PRESSURE, AND MODULATION OF HEART RATE BY S1P

Neither blood pressure nor cardiac function (as evaluated in situ using a Millar catheter) are altered in S1P2-deficient mice under baseline or stimulated con-ditions (105). Blood pressure is also normal in S1P3-deficient mice (104). However, cardiomyocyte-restricted deletion of S1P1 leads to the progressive development of heart failure and premature death; the underlying defect is a profound perturbation of cardiomyocyte Na+ and Ca2+ homeostasis caused by the inactivation of the Na+/H+ exchanger (NHE-1), a previously unknown target of S1P signaling in the heart (manuscript submitted). Thus, S1P1 is indis-pensable for normal, physiological heart function.

Data are sparse on the putative roles of S1P in cardiomyocyte hypertrophy, and they stem only from in vitro studies. S1P has been known as a trophic factor for cardiomyocytes as it induces protein synthesis and cellular hyper-trophy (110). Furthermore, S1P activates the MAPK and STAT3 pathways in cardiomyocytes (111), both of which are implicated in the physiological hyper-trophic response (112). Cardiomyocytes from S1P3, but not S1P2, receptor knockout mice have lost their ability to activate PLC in response to S1P (113). As Gq signaling and pressure overload-induced hypertrophy are closely associ-ated in vivo, it has been postulated that S1P3 receptor/Gq/PLC activation may thus contribute to the cardiac hypertrophic response in vivo, although this has not been experimentally corroborated (113). In agreement, S1P3 is the recep-tor by which exogenous S1P increases intracellular Ca2+ concentration and induces nuclear export of HDAC4 and nuclear import of NFAT, respectively,


in cardiomyocytes in vitro (manuscript submitted), which is important for the activation of the hypertrophic gene expression program. In contrast, S1P1 is causally involved in the pathological response of the heart to pressure over-load in vivo as treatment with the selective S1P1 antagonist W146 improved cardiac function and ameliorated pathological cardiac remodeling after trans-aortic constriction (manuscript submitted).

S1P has been shown to exert different effects on ion currents in cardiomyo-cytes in vitro. It stimulates the inward rectifier potassium current (IK.ACh) resulting in a reduction of spontaneous pacing rate (114) and inhibits the isoproterenol-induced increase in currents through L-type calcium channels (ICa,L), as well as the hyperpolarization-activated inward current (If), thereby attenuating the positive chronotropic effects of β-adrenergic stimuli in sino-atrial node cells and ventricular myocytes (114, 115).

In vivo, S1P receptors are involved in the control of heart rate. FTY720-phosphate, which acts as a functional antagonist on S1P1 and likely other S1P receptors (116), induces an acute and transient bradycardia in mice and men (117, 118). Experimental studies suggest that both S1P1 and S1P3 agonism prior to receptor internalization is involved in the process (117, 119, 120). However, species differences have also been observed, including S1P receptor subtype differences affecting heart rate between mouse (117) and human (116). These differences may in part explain the absence of related cardiac alterations in humans exposed for up to 7 years to FTY720 (fingolimod).

14.9. S1P IN ATHEROSCLEROSIS: MONOCYTE ADHESION AND ENDOTHELIAL PERMEABILITY

Monocyte adhesion to activated endothelium is a key step in the pathogenesis of atherosclerosis. S1P suppresses the adherence of inflammatory cells to TNFα-activated aortic endothelium in vivo through inhibition of IL-8 and MCP-1 (121). In diabetic NOD mice, S1P and S1P1 agonists have been shown to abrogate monocytic cell adhesion to aortic endothelium in part through a NO-dependent mechanism and VCAM-1 inhibition due to the suppression of NF-κB (122). In contrast, S1P generated by TNFα-stimulated Sphk1 induced the expression of adhesion molecules, while exogenous S1P application stimu-lated VCAM-1 and E-selectin via the transcriptional activation of NF-κB (123–126). Also, chronic overexpression of Sphk1 has been shown to lead to a higher constitutive and TNFα-stimulated expression of VCAM-1 (127). Sphk1 has also been implicated in the induction of COX-2 by TNFα and the production of inflammatory prostaglandins such as PGE2 (128). Knockdown of S1P phosphatase and S1P lyase has been shown to augment prostaglandin production (128), suggesting that S1P mediates COX-2-dependent proinflam-matory effects of cytokines. A conciliation of such different observations must take into account the effects that different S1P receptors may have on differ-ent adhesion molecules, yet unknown intracellular S1P effects on adhesion, as well as the fact that supraphysiological levels of S1P may inhibit the same

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processes that physiological concentrations can activate (29). In agreement, S1P has been shown to induce endothelial VCAM-1 and E-selectin expression at concentrations of 5–20 µmol/L (124, 125), while nanomolar concentrations inhibited VCAM-1 (122); an increase of S1P to 5 µmol/L in the same study led to higher monocyte adhesion (122). Thus, the effect of endogenously pro-duced S1P following cytokine stimulation may differ from that of S1P applied exogenously on already cytokine-stimulated endothelial cells, and the amounts of S1P available for signaling are very important.

Endothelial cell permeability and the tightness of the endothelial lining are also major factors in subendothelial lipid deposition and leukocyte transmigra-tion in atherosclerosis. S1P decreases endothelial permeability and seals the endothelial barrier by promoting adherens junction assembly (59, 129, 130). While S1P1 and S1P3 both strengthen the formation of endothelial cell junc-tions (129, 131, 132), S1P2 weakens them through signaling via Rho–ROCK and the PIP3 phosphatase PTEN (phosphatase and tensin homolog) (133–135). The S1P pool required for the maintenance of the endothelial barrier stems from the plasma compartment. This has been shown in “pS1Pless” mice that lack S1P in plasma and display vascular leakage (136); both transfusion of erythrocytes and S1P1 receptor agonists reversed the leakage (136). However, other S1P sources are also present, such as endothelial cells, which produce and secrete S1P when exposed to physiological laminar shear stress (4). The global knockout of Sphk1 exhibits a similar, although less severe, leakage phenotype despite unaltered plasma S1P levels (137). The receptors respon-sible for endothelial tightness have also been identified: S1P1 is required for the maintenance of endothelial integrity as S1P1 antagonists induce capillary leakage in the lung, kidney, skin, and intestine (39, 138, 139). Thus, plasma levels of S1P regulate vascular permeability by acting on S1P receptors (45). In lipo-polysaccharide (LPS) or protease-activated receptor 1 (PAR1)-induced inflam-matory lung injury, vascular permeability is increased; however, as same agents also stimulate Sphk1, gradually increasing S1P production reseals the endo-thelial cell barrier via S1P1 in a counterregulatory manner (140, 141). Further-more, the barrier-enhancing functions of activated protein C (APC) can be partially attributed to the activation of Sphk1, production of S1P, and subse-quent engagement of S1P1 (142) or even direct transactivation of S1P1 by the APC receptor (143). Finally, administration of S1P1 agonists has been shown to protect mice devoid of plasma S1P from platelet-activating factor (PAF)-induced generalized vascular leakage and death (136).

14.10. S1P IN ATHEROSCLEROSIS: LESSONS FROM S1P RECEPTOR AGONISTS AND KNOCKOUT MICE

Despite the profound and multiple roles that S1P plays in the biology of all the vascular and nonvascular cell types that are involved in the pathogen-esis of atherosclerosis—or maybe exactly for these reasons—its role in the pathogenesis of atherosclerosis is still unknown. The most direct evidence has


come from studies that have employed FTY720 in different mouse models of atherosclerosis and from studies with S1P receptor knockouts on an atherosclerosis-susceptible background.

The effect of FTY720 on atherosclerosis has been elucidated in three inde-pendent studies. Two of them have shown FTY720 to attenuate the develop-ment of atherosclerotic lesions in apolipoprotein E (ApoE)-deficient mice (144) and LDL receptor-deficient (LDL-R) mice (145), respectively—the two most widely used mouse models of atherosclerosis. The third study observed no effect on plaque size, but the higher FTY720 dose that was used provoked hypercholesterolemia of unknown origin (146)—an effect not observed by the other two—which may have obscured any antiatherogenic effects. The mecha-nism of atheroprotection by FTY720 is difficult to pin down. Treatment with FTY720 impacts several biological processes that are known to play a role in atherosclerosis and may thus potentially contribute to its inhibitory effect of atherosclerotic lesion development. FTY720 stimulates nitric oxide (NO) pro-duction in endothelial cells (147), inhibits the generation of ROS, and reduces the production and release of inflammatory chemokines such as monocyte chemoattractant protein 1 (MCP-1) (144, 148). Plasma levels of the cytokines TNFα, IL-6, IL-12, and IFNγ are reduced in LDL-R-deficient mice treated with FTY70 (145), suggesting possible impairment in the communication between lymphocytes and monocyte/macrophages. None of these FTY720 actions can be made solely or causally responsible for its atheroprotective effect. Finally, it may be simply due to the profound inhibition of lymphocyte homeostasis, which would be perfectly in line with the important role that immunological processes in general, and T-lymphocytes in particular, play in the pathogenesis of atherosclerosis (149). Atherosclerosis is a chronic inflam-matory disease that strongly depends on T-lymphocyte-mediated adaptive immune responses for its initiation and progression (149). Atherosclerotic plaques contain activated CD4+ T cells of the T helper 1 (TH1)-phenotype that induce the expression of numerous cytokines important in lesion progression and destabilization (150). An impaired immunological response by FTY720 may thus result in defects in T-cell/macrophage communication as well as compromised antigen processing and presentation. As FTY720 has been shown to bias T-cell immune responses toward TH2 by suppressing major dendritic cell effector functions (151), this may not only play a role in allograft-induced immune responses but also in atherosclerosis, where TH2-cell responses have been implicated in atheroprotection (149). Thus, atheroprotection by FTY720 may be simply due to immunosuppression. Its promiscuous activation of four out of the five S1P receptors, its different receptor desensitization kinetics from that of S1P (152), and the fact that it overrides the significance of any biological S1P gradient do not allow extrapolating the FTY720 effects on atherosclerosis to any potential effects endogenous S1P and its receptors may have on the disease.

In contrast, studies on the role of individual S1P receptors in atherosclerosis have just recently unveiled their important contributions. Three studies have

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looked at the role of S1P2 and S1P3, respectively, by studying their knockouts in an ApoE-deficient background (153–155). The two studies to address S1P2 have shown a clear reduction in atherosclerotic plaque burden, a reduced macrophage density, and an increased VSMC content in atherosclerotic lesions of S1P2/ApoE double-knockout mice (153, 154). While some endothelial cell properties of S1P2-deficient mice, such as increased phospho-eNOS in aortas may have contributed to the effect, the main cause—as show by both studies—is the impact of S1P2 deficiency on macrophages. Bone marrow transplantation preformed in both studies has shown that atherosclerosis is greatly attenuated in S1P2-deficient bone marrow chimera. Along with these in vivo data, several atherosclerosis-relevant properties of S1P2

–/– macrophages were altered: S1P2-deficient macrophages showed a reduced ability to take up modified LDL at least in one study (153) (although not in the other; see Reference 154), had a higher propensity for cholesterol efflux, and exhibited a reduced phagocytotic activity (153). In addition, S1P2 on macrophages acts as a chemorepellent receptor in vitro. This is supported by evidence that S1P2-deficient mice recruit more macrophages in a peritonitis model and that absence of S1P2 abrogates the ability of S1P to inhibit macrophage migration to C5a and CXCL12 in vitro (156). Thus, the current understanding is that S1P2 is a proatherogenic receptor that enhances lipid uptake and reduces lipid efflux, respectively, in macrophages and promotes phagocytosis, which all leads to higher lipid accu-mulation in the artery wall. The chemorepulsive action of S1P2 may promote monocyte/macrophage immigration and retention in the lesion after entry (if, indeed, the plaque has a lower S1P concentration than plasma, which still needs to be shown experimentally).

The role of S1P3 in atherosclerosis has also been examined in the ApoE background (155). S1P3 deficiency did not affect atherosclerotic lesion size per se but greatly reduced the lesional monocyte/macrophage content. Bone marrow transplantation studies showed that S1P3 expression both in hemato-poietic and nonhematopoietic cells contributed to the altered monocyte/macrophage accumulation. S1P3-deficient mice had a defect in macrophage recruitment as observed in the thioglycollate-induced peritonitis model and S1P was shown to be chemotactic for wild type but not S1P3-deficient perito-neal macrophages (155). Finally, FTY720 inhibited macrophage recruitment into the inflamed peritoneum. The conclusion made in this study is that S1P3 is required for monocyte/macrophage recruitment to atherosclerotic lesions. In contrast, S1P1 does not appear to play a role in macrophage recruitment to the peritoneum as shown using S1P1 hematopoietic chimeras (156) and con-ditional deletion of S1P1 in myeloid cells (155). In summary, these data suggest a scenario in which S1P2 and S1P3 drive macrophages toward sites of inflam-mation such as the peritoneum or atherosclerotic lesions by chemorepulsion from plasma and chemoattraction into the lesion, respectively.

The effects of S1P receptor signaling on the inflammatory potential of macrophages are more obscure and are still not well understood. One study showed reduced serum IL-1β and IL-18 levels but no changes in TNFα


in S1P2-deficient mice challenged with LPS (154). Another study showed less TNFα expression in response to S1P, as well as less p65 NF-κB subunit phos-phorylation in S1P2-deficient macrophages in vitro, together with lower TNFα, IL-6, IFN-γ, and MCP-1 mRNA expression in aortas of S1P2/ApoE double-knockout mice in vivo (153). However, gene expression was normalized to CD3 and not to a macrophage-specific gene in that study, and lower expression may thus have been a function of smaller lesion size (153). A third study sug-gested that S1P inhibits LPS/IFN-γ-stimulated cytokine production in macro-phages in vitro via S1P1, while S1P2 promoted cytokine expression (157). Yet another study has found no effects of S1P on basal or LPS/IFN-γ-stimulated cytokine expression but a blunted induction of MCP-1 in response to LPS in S1P3-deficient macrophages in vitro, and a reduced basal TNFα and MCP-1 expression in peritoneal macrophages in vivo (155). These differences could potentially be attributed to the different tissue sources of the macrophages used in the different studies as well as their different activation and/or dif-ferentiation states. For instance, the responsiveness of thioglycollate-elicited inflammatory macrophages to exogenous S1P may differ from that of bone marrow-derived macrophages that have been generated by long-term culture with M-CSF. In summary, there is currently no uniform model of how S1P affects the inflammatory cytokine profile of macrophages. Instead, differences in macrophage source, differentiation, and stimulation as well as the net effect of simultaneously occurring S1P and cytokine signaling must be taken into consideration when interpreting different macrophage studies on S1P in the context of atherosclerosis.

14.11. S1P EFFECTS ON VSMCS AND THEIR IMPACT ON RESTENOSIS AFTER INJURY AND ARTERIAL REMODELING

The atherosclerosis studies mentioned above have all shown that the VSMC content of atherosclerotic lesions was increased in the absence of S1P2 and S1P3, respectively, as well as following FTY720 treatment. An increased VSMC content in lesions is normally associated with more stable plaque morphology (at least in humans) and presumably prevents plaque rupture. Whether the increased lesional VSMC content in the global S1P2 and S1P3 receptor knock-outs arises from direct or indirect S1P effects cannot be followed from these studies. However, S1P clearly influences VSMC behavior and phenotype in vitro and in vivo. The current consensus on the effect of S1P on migration is that it inhibits VSMC migration toward potent chemotactic stimuli such as PDGF-BB in mouse, rat, and human VSMC in vitro, and that this effect is mediated by inhibition of Rac1 activation by S1P2 (61, 158, 159). Less clear is whether S1P itself is a chemotactic agent for VSMC: While most studies have found this is not the case (61, 158, 159), one study did (153). However, there is agreement on the effect that a loss of S1P2 signaling has on migration: S1P2-deficient VSMCs migrate faster to S1P and PDGF-BB than wild-type cells

S1P EffECtS 299

in vitro (153, 160). A reconciling explanation is that S1P2 presumably serves as an important brake on migration that becomes more visible the greater the chemotactic stimulus is (e.g., S1P vs. PDGF-BB).

The data on putative proliferation-promoting effects of S1P on VSMC differ in the literature. No effect of S1P on proliferation has been described for both human and mouse VSMC (155, 158). In contrast, S1P promoted pro-liferation in rat VSMCs, where it was abolished by an S1P1/S1P3 inhibitor, but not an S1P2 inhibitor (161). In vitro, S1P2-deficient VSMCs did not show altered proliferation in one study (160) but had an enhanced proliferation in another (153). S1P3-deficient VSMCs have neither altered proliferation nor migration as examined in vitro (155).

VSMC differentiation is a key component of atherosclerotic lesions, where the contractile quiescent phenotype of medial VSMC turns into the highly synthetic or migratory phenotype of VSMC within lesions. A causal stimulus for this plasticity is vascular injury. As a consequence, medial VSMCs down-regulate the expression of contractile genes, migrate to the newly forming VSMC-rich intima (neointima), and proliferate there. In this process, the tran-scriptional repression of VSMC-specific differentiation genes plays a crucial role. Such genes are SMα-actin, smooth muscle myosin heavy chain (SMMHC), and SM22α, which all have a CArG box in their promoters to which serum response factor (SRF) and myocardin or myocardin-related transcription factors (MRTFs) bind. S1P has been shown to increase expression of these VSMC differentiation marker genes through a RhoA/MRTF-dependent pathway (161). S1P receptors play an important role in this process: S1P2 promotes and S1P1/S1P3 inhibit the S1P-induced activation of SMα-actin and SMMHC, and a crucial role in this process has been attributed to L-type voltage-gated Ca2+ channels and RhoA/Rho kinase-dependent SRF enrich-ment of CArG box promoter regions (161, 162). Finally, VSMCs from different vascular beds and different differentiation states (medial vs. neointimal VSMC; see Reference 49) have different expression levels of S1P receptors, which all needs to be considered when comparing S1P effects in different VSMC-related settings.

All processes by which S1P affects VSMC function—migration, prolifera-tion, and differentiation—jointly determine the effect of S1P receptor signal-ing after arterial wall injury in vivo. This was addressed by only a few studies: One study has shown that administration of an S1P1/S1P3 antagonist inhibited neointima formation after balloon injury of the carotid in rats (161); two others have shown that neointima formation after carotid ligation was greatly enhanced in S1P2

–/– (160) and S1P3–/– mice (155), respectively. As inferred from

the in vitro data, several mechanisms could be instrumental in the inhibition of neointimal growth by S1P2: S1P signaling via S1P2 may not only be blocking VSMC migration from the media into the intima but, by promoting VSMC differentiation, may be limiting the extent by which neointimal VSMC responds to proliferative stimuli (162). The reasons for increased neointima formation in S1P3

–/– mice after carotid ligation are not yet known as S1P3-deficient VSMCs


have neither altered in vitro proliferation nor migration (155). However, the genetic background is known to determine the responsiveness of a mouse strain to vascular injury. This may be one reason for the observed differences in S1P effects on neointima formation and vascular remodeling among mouse stains and in comparison to the rat. Mouse lines such as FVB have a tendency to a larger neointima formation than C57/Bl6 mice who also have lower S1P2 and higher S1P1 expression in the arterial wall, respectively (160). Another reason could be the regulation of S1P receptor expression after vascular injury: In the rat carotid wire injury model, there is an early (within hours) and sub-stantial increase of S1P1 gene expression and a smaller one of S1P3 (161), while no major differences (except for a moderate induction of S1P3) have been observed in the carotid ligation model (162).

14.12. PLASMA S1P CONCENTRATIONS INSIDE AND OUTSIDE OF HDL ARE ALTERED IN HUMAN CORONARY ARTERY DISEASE (CAD) AND MYOCARDIAL INFARCTION

Any measurements of plasma S1P need to take into account the strong posi-tive correlation between S1P and the plasma HDL-C level, and the fact that 70–90% of plasma S1P is associated with the HDL fraction (13, 14). Thus, any changes in HDL levels will inevitably alter S1P levels in plasma. Therefore, studies that examine plasma S1P in human subjects must normalize plasma S1P levels to the plasma HDL-C concentration.

S1P levels in plasma and those associated with HDL have been shown to be altered in patients with CAD. The first study to address S1P in CAD shows a positive association between total serum S1P and the severity of CAD as determined by the scoring of coronary stenosis (163). The second and third studies have looked at total plasma S1P and the S1P contained in the HDL fraction in healthy individuals, in patients with stable CAD (164, 165), and in patients with AMI (164). HDL-C-normalized plasma S1P levels were higher in CAD than in controls, and even higher in AMI. The S1P amount contained in isolated HDL from CAD patients was also lower than in controls. Early during AMI, S1P concentrations both in plasma and in HDL acutely increased to levels even higher than controls, suggesting S1P release of yet unknown origin and its uptake by plasma HDL. Finally, the S1P pool in plasma bound to HDL was higher and that bound to HDL lower, respectively, in CAD patients compared with controls. This suggests that HDL from CAD patients may have a defect in taking up or retaining S1P. This non-HDL-bound plasma S1P pool is able to discriminate patients with MI and sCAD from controls (164), fulfilling the definition of a biomarker. In cardiovascular medicine, it is well established that HDL that stems from patients with CAD are impaired in respect to several of their potentially beneficial properties such as the general anti-inflammatory, antioxidative, and vasodilatory characteristics of HDL (166). The established contribution of the S1P content of HDL to these

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properties (14) suggests that the lower amount of HDL-bound S1P in CAD patients may comprise an important part of their HDL dysfunction. Thus, any intervention aimed to increase the uptake of S1P into HDL may help to restore HDL function by increasing their beneficial S1P content and, at the same time, help to decrease the amount of free, non-HDL-bound del-eterious S1P.

14.13. FUTURE PERSPECTIVES

It has become clear that S1P, its receptors, and the enzymes determining its metabolism have important roles both in cardiovascular homeostasis and disease. Experimental evidence from in vitro and in vivo studies suggests that pharmacological interference with S1P signaling and metabolism may offer novel approaches to cardiovascular diseases. The attractiveness of S1P-based drugs for cardiovascular applications is underscored by the possibility of their rapid implementation in the clinical situation as FTY720 (fingolimod) has already been approved by the FDA and the European Commission for the treatment of multiple sclerosis. This would certainly expedite approval if they prove efficient in the treatment of cardiovascular diseases and/or offer addi-tional benefits to established therapies. Nevertheless, a number of potentially important but incompletely understood relationships between S1P and car-diovascular diseases still remain. S1P1 gene polymorphisms have been associ-ated with CAD and stroke (167, 168), and plasma pools of S1P are altered in CAD and myocardial infarction (164). They offer new potential implications for diagnosis, follow-up, and prediction of adverse cardiovascular events that will need to be addressed by future studies.

REFERENCES

1. Okajima F. 2002. Plasma lipoproteins behave as carriers of extracellular sphingo-sine 1-phosphate: is this an atherogenic mediator or an anti-atherogenic media-tor? Biochim Biophys Acta 1582:132–137.

2. Zhang B, Tomura H, Kuwabara A, Kimura T, Miura S, et al. 2005. Correlation of high density lipoprotein (HDL)-associated sphingosine 1-phosphate with serum levels of HDL-cholesterol and apolipoproteins. Atherosclerosis 178:199–205.

3. Pappu R, Schwab SR, Cornelissen I, Pereira JP, Regard JB, et al. 2007. Promotion of lymphocyte egress into blood and lymph by distinct sources of sphingosine-1-phosphate. Science 316:295–298.

4. Venkataraman K, Lee YM, Michaud J, Thangada S, Ai Y, et al. 2008. Vascular endothelium as a contributor of plasma sphingosine 1-phosphate. Circ Res 102:669–676.

5. Hannun YA, Obeid LM. 2008. Principles of bioactive lipid signalling: lessons from sphingolipids. Nat Rev Mol Cell Biol 9:139–150.


6. van Meer G, Voelker DR, Feigenson GW. 2008. Membrane lipids: where they are and how they behave. Nat Rev Mol Cell Biol 9:112–124.

7. Kobayashi N, Nishi T, Hirata T, Kihara A, Sano T, et al. 2006. Sphingosine 1-phosphate is released from the cytosol of rat platelets in a carrier-mediated manner. J Lipid Res 47:614–621.

8. Mitra P, Oskeritzian CA, Payne SG, Beaven MA, Milstien S, Spiegel S. 2006. Role of ABCC1 in export of sphingosine-1-phosphate from mast cells. Proc Natl Acad Sci U S A 103:16394–16399.

9. Kobayashi N, Yamaguchi A, Nishi T. 2009. Characterization of the ATP-dependent sphingosine 1-phosphate transporter in rat erythrocytes. J Biol Chem 284:21192–21200.

10. Lee YM, Venkataraman K, Hwang SI, Han DK, Hla T. 2007. A novel method to quantify sphingosine 1-phosphate by immobilized metal affinity chromatography (IMAC). Prostaglandins Other Lipid Mediat 84:154–162.

11. Kawahara A, Nishi T, Hisano Y, Fukui H, Yamaguchi A, Mochizuki N. 2009. The sphingolipid transporter spns2 functions in migration of zebrafish myocardial precursors. Science 323:524–527.

12. Osborne N, Brand-Arzamendi K, Ober EA, Jin SW, Verkade H, et al. 2008. The spinster homolog, two of hearts, is required for sphingosine 1-phosphate signaling in zebrafish. Curr Biol 18:1882–1888.

13. Murata N, Sato K, Kon J, Tomura H, Yanagita M, et al. 2000. Interaction of sphin-gosine 1-phosphate with plasma components, including lipoproteins, regulates the lipid receptor-mediated actions. Biochem J 352(Pt 3):809–815.

14. Sattler K, Levkau B. 2009. Sphingosine-1-phosphate as a mediator of high-density lipoprotein effects in cardiovascular protection. Cardiovasc Res 82:201–211.

15. Kontush A, Therond P, Zerrad A, Couturier M, Negre-Salvayre A, et al. 2007. Preferential sphingosine-1-phosphate enrichment and sphingomyelin depletion are key features of small dense HDL3 particles: relevance to antiapoptotic and antioxidative activities. Arterioscler Thromb Vasc Biol 27:1843–1849.

16. Bode C, Sensken SC, Peest U, Beutel G, Thol F, et al. 2010. Erythrocytes serve as a reservoir for cellular and extracellular sphingosine 1-phosphate. J Cell Biochem 109:1232–1243.

17. Sevvana M, Ahnstrom J, Egerer-Sieber C, Lange HA, Dahlback B, Muller YA. 2009. Serendipitous fatty acid binding reveals the structural determinants for ligand recognition in apolipoprotein M. J Mol Biol 393:920–936.

18. Christoffersen C, Obinata H, Kumaraswamy SB, Galvani S, Ahnstrom J, et al. 2011. Endothelium-protective sphingosine-1-phosphate provided by HDL-associated apolipoprotein M. Proc Natl Acad Sci U S A 108:9613–9618.

19. Mandala S, Hajdu R, Bergstrom J, Quackenbush E, Xie J, et al. 2002. Alteration of lymphocyte trafficking by sphingosine-1-phosphate receptor agonists. Science 296:346–349.

20. Argraves KM, Wilkerson BA, Argraves WS, Fleming PA, Obeid LM, Drake CJ. 2004. Sphingosine-1-phosphate signaling promotes critical migratory events in vasculogenesis. J Biol Chem 279:50580–50590.

21. Wendler CC, Rivkees SA. 2006. Sphingosine-1-phosphate inhibits cell migration and endothelial to mesenchymal cell transformation during cardiac development. Dev Biol 291:264–277.

REfERENCES 303

22. Vessey DA, Kelley M, Li L, Huang Y. 2009. Sphingosine protects aging hearts from ischemia/reperfusion injury: superiority to sphingosine 1-phosphate and ischemic pre- and post-conditioning. Oxid Med Cell Longev 2:146–151.

23. Johnson KR, Johnson KY, Becker KP, Bielawski J, Mao C, Obeid LM. 2003. Role of human sphingosine-1-phosphate phosphatase 1 in the regulation of intra- and extracellular sphingosine-1-phosphate levels and cell viability. J Biol Chem 278:34541–34547.

24. Mandala SM, Thornton R, Galve-Roperh I, Poulton S, Peterson C, et al. 2000. Molecular cloning and characterization of a lipid phosphohydrolase that degrades sphingosine-1- phosphate and induces cell death. Proc Natl Acad Sci U S A 97:7859–7864.

25. Zhou J, Saba JD. 1998. Identification of the first mammalian sphingosine phos-phate lyase gene and its functional expression in yeast. Biochem Biophys Res Commun 242:502–507.

26. Bandhuvula P, Honbo N, Wang GY, Jin ZQ, Fyrst H, et al. 2011. S1P lyase: a novel therapeutic target for ischemia-reperfusion injury of the heart. Am J Physiol Heart Circ Physiol 300:H1753–H1761.

27. Salomone S, Soydan G, Ip PC, Hopson KM, Waeber C. 2010. Vessel-specific role of sphingosine kinase 1 in the vasoconstriction of isolated basilar arteries. Phar-macol Res 62:465–474.

28. Peter BF, Lidington D, Harada A, Bolz HJ, Vogel L, et al. 2008. Role of sphingosine-1-phosphate phosphohydrolase 1 in the regulation of resistance artery tone. Circ Res 103:315–324.

29. Rivera R, Chun J. 2008. Biological effects of lysophospholipids. Rev Physiol Biochem Pharmacol 160:25–46.

30. Spiegel S, Milstien S. 2003. Sphingosine-1-phosphate: an enigmatic signalling lipid. Nat Rev Mol Cell Biol 4:397–407.

31. Olivera A, Spiegel S. 1993. Sphingosine-1-phosphate as second messenger in cell proliferation induced by PDGF and FCS mitogens. Nature 365:557–560.

32. Hobson JP, Rosenfeldt HM, Barak LS, Olivera A, Poulton S, et al. 2001. Role of the sphingosine-1-phosphate receptor EDG-1 in PDGF-induced cell motility. Science 291:1800–1803.

33. Waters C, Sambi B, Kong KC, Thompson D, Pitson SM, et al. 2003. Sphingosine 1-phosphate and platelet-derived growth factor (PDGF) act via PDGF beta receptor-sphingosine 1-phosphate receptor complexes in airway smooth muscle cells. J Biol Chem 278:6282–6290.

34. Tanimoto T, Jin ZG, Berk BC. 2002. Transactivation of vascular endothelial growth factor (VEGF) receptor Flk-1/KDR is involved in sphingosine 1-phosphate- stimulated phosphorylation of Akt and endothelial nitric-oxide synthase (eNOS). J Biol Chem 277:42997–43001.

35. Walter DH, Rochwalsky U, Reinhold J, Seeger F, Aicher A, et al. 2007. Sphingosine-1-phosphate stimulates the functional capacity of progenitor cells by activation of the CXCR4-dependent signaling pathway via the S1P3 receptor. Arterioscler Thromb Vasc Biol 27:275–282.

36. Ryser MF, Ugarte F, Lehmann R, Bornhauser M, Brenner S. 2008. S1P(1) over-expression stimulates S1P-dependent chemotaxis of human CD34+ hematopoietic


progenitor cells but strongly inhibits SDF-1/CXCR4-dependent migration and in vivo homing. Mol Immunol 46:166–171.

37. Kimura T, Boehmler AM, Seitz G, Kuci S, Wiesner T, et al. 2004. The sphingosine 1-phosphate receptor agonist FTY720 supports CXCR4-dependent migration and bone marrow homing of human CD34+ progenitor cells. Blood 103:4478–4486.

38. Xin C, Ren S, Kleuser B, Shabahang S, Eberhardt W, et al. 2004. Sphingosine 1-phosphate cross-activates the Smad signaling cascade and mimics transforming growth factor-beta-induced cell responses. J Biol Chem 279:35255–35262.

39. Rosen H, Gonzalez-Cabrera P, Marsolais D, Cahalan S, Don AS, Sanna MG. 2008. Modulating tone: the overture of S1P receptor immunotherapeutics. Immunol Rev 223:221–235.

40. Alewijnse AE, Peters SL, Michel MC. 2004. Cardiovascular effects of sphingosine-1-phosphate and other sphingomyelin metabolites. Br J Pharmacol 143:666–684.

41. Mazurais D, Robert P, Gout B, Berrebi-Bertrand I, Laville MP, Calmels T. 2002. Cell type-specific localization of human cardiac S1P receptors. J Histochem Cyto-chem 50:661–670.

42. Ozaki H, Hla T, Lee MJ. 2003. Sphingosine-1-phosphate signaling in endothelial activation. J Atheroscler Thromb 10:125–131.

43. Alewijnse AE, Peters SL. 2008. Sphingolipid signalling in the cardiovascular system: good, bad or both? Eur J Pharmacol 585:292–302.

44. Saba JD, Hla T. 2004. Point-counterpoint of sphingosine 1-phosphate metabolism. Circ Res 94:724–734.

45. Skoura A, Hla T. 2009. Regulation of vascular physiology and pathology by the S1P2 receptor subtype. Cardiovasc Res 82:221–228.

46. Levkau B. 2008. Sphingosine-1-phosphate in the regulation of vascular tone: a finely tuned integration system of S1P sources, receptors, and vascular responsive-ness. Circ Res 103:231–233.

47. Igarashi J, Michel T. 2009. Sphingosine-1-phosphate and modulation of vascular tone. Cardiovasc Res 82:212–220.

48. Coussin F, Scott RH, Wise A, Nixon GF. 2002. Comparison of sphingosine 1-phosphate-induced intracellular signaling pathways in vascular smooth muscles: differential role in vasoconstriction. Circ Res 91:151–157.

49. Kluk MJ, Hla T. 2001. Role of the sphingosine 1-phosphate receptor EDG-1 in vascular smooth muscle cell proliferation and migration. Circ Res 89:496–502.

50. Kupperman E, An S, Osborne N, Waldron S, Stainier DY. 2000. A sphingosine-1-phosphate receptor regulates cell migration during vertebrate heart development. Nature 406:192–195.

51. Ishii I, Ye X, Friedman B, Kawamura S, Contos JJ, et al. 2002. Marked perinatal lethality and cellular signaling deficits in mice null for the two sphingosine 1-phosphate (S1P) receptors, S1P(2)/LP(B2)/EDG-5 and S1P(3)/LP(B3)/EDG-3. J Biol Chem 277:25152–25159.

52. Liu Y, Wada R, Yamashita T, Mi Y, Deng CX, et al. 2000. Edg-1, the G protein-coupled receptor for sphingosine-1-phosphate, is essential for vascular matura-tion. J Clin Invest 106:951–961.

53. MacLennan AJ, Carney PR, Zhu WJ, Chaves AH, Garcia J, et al. 2001. An essential role for the H218/AGR16/Edg-5/LP(B2) sphingosine 1-phosphate receptor in neuronal excitability. Eur J Neurosci 14:203–209.

REfERENCES 305

54. Allende ML, Proia RL. 2002. Sphingosine-1-phosphate receptors and the develop-ment of the vascular system. Biochim Biophys Acta 1582:222–227.

55. Mizugishi K, Yamashita T, Olivera A, Miller GF, Spiegel S, Proia RL. 2005. Essen-tial role for sphingosine kinases in neural and vascular development. Mol Cell Biol 25:11113–11121.

56. Rosen H, Gonzalez-Cabrera PJ, Sanna MG, Brown S. 2009. Sphingosine 1-phosphate receptor signaling. Annu Rev Biochem 78:743–768.

57. Hla T. 2004. Physiological and pathological actions of sphingosine 1-phosphate. Semin Cell Dev Biol 15:513–520.

58. Hla T, Lee MJ, Ancellin N, Paik JH, Kluk MJ. 2001. Lysophospholipids—receptor revelations. Science 294:1875–1878.

59. Lee MJ, Thangada S, Claffey KP, Ancellin N, Liu CH, et al. 1999. Vascular endo-thelial cell adherens junction assembly and morphogenesis induced by sphingosine-1-phosphate. Cell 99:301–312.

60. Kono M, Mi Y, Liu Y, Sasaki T, Allende ML, et al. 2004. The sphingosine-1- phosphate receptors S1P1, S1P2, and S1P3 function coordinately during embry-onic angiogenesis. J Biol Chem 279:29367–29373.

61. Ryu Y, Takuwa N, Sugimoto N, Sakurada S, Usui S, et al. 2002. Sphingosine-1-phosphate, a platelet-derived lysophospholipid mediator, negatively regulates cellular Rac activity and cell migration in vascular smooth muscle cells. Circ Res 90:325–332.

62. Skoura A, Sanchez T, Claffey K, Mandala SM, Proia RL, Hla T. 2007. Essential role of sphingosine 1-phosphate receptor 2 in pathological angiogenesis of the mouse retina. J Clin Invest 117:2506–2516.

63. Michaud MD, Robitaille GA, Gratton JP, Richard DE. 2009. Sphingosine-1- phosphate: a novel nonhypoxic activator of hypoxia-inducible factor-1 in vascular cells. Arterioscler Thromb Vasc Biol 29:902–908.

64. Visentin B, Vekich JA, Sibbald BJ, Cavalli AL, Moreno KM, et al. 2006. Validation of an anti-sphingosine-1-phosphate antibody as a potential therapeutic in reduc-ing growth, invasion, and angiogenesis in multiple tumor lineages. Cancer Cell 9:225–238.

65. Xie B, Shen J, Dong A, Rashid A, Stoller G, Campochiaro PA. 2009. Blockade of sphingosine-1-phosphate reduces macrophage influx and retinal and choroidal neovascularization. J Cell Physiol 218:192–198.

66. Karliner JS. 2006. Toward solving the riddle: the enigma becomes less mysterious. Circ Res 99:465–467.

67. Vessey DA, Kelley M, Li L, Huang Y, Zhou HZ, et al. 2006. Role of sphingosine kinase activity in protection of heart against ischemia reperfusion injury. Med Sci Monit 12:BR318–BR324.

68. Theilmeier G, Schmidt C, Herrmann J, Keul P, Schafers M, et al. 2006. High-density lipoproteins and their constituent, sphingosine-1-phosphate, directly protect the heart against ischemia/reperfusion injury in vivo via the S1P3 lysophospholipid receptor. Circulation 114:1403–1409.

69. Karliner JS. 2009. Sphingosine kinase and sphingosine 1-phosphate in cardiopro-tection. J Cardiovasc Pharmacol 53:189–197.

70. Jin ZQ, Goetzl EJ, Karliner JS. 2004. Sphingosine kinase activation mediates ischemic preconditioning in murine heart. Circulation 110:1980–1989.


71. Lecour S, Smith RM, Woodward B, Opie LH, Rochette L, Sack MN. 2002. Iden-tification of a novel role for sphingolipid signaling in TNF alpha and ischemic preconditioning mediated cardioprotection. J Mol Cell Cardiol 34:509–518.

72. Jin ZQ, Zhang J, Huang Y, Vessey DA, Karliner JS. 2005. A sphingosine kinase 1 mutation sensitizes the myocardium to ischemia/reperfusion injury and abrogates ischemic preconditioning. Circ Res 97:1204 (Abstract).

73. Duan HF, Wang H, Yi J, Liu HJ, Zhang QW, et al. 2007. Adenoviral gene transfer of sphingosine kinase 1 protects heart against ischemia/reperfusion-induced injury and attenuates its postischemic failure. Hum Gene Ther 18:1119–1128.

74. Vessey DA, Li L, Jin Z, Kelley M, Honbo N, Zhang J, Karliner JS. 2011. A sphin-gosine kinase form 2 knockout sensitizes mouse myocardium to ischemia/reoxygenation injury and diminishes responsiveness to ischemic preconditioning. Oxid Med Cell Longev 2011:Article ID 961059:1–8.

75. Hausenloy DJ, Yellon DM. 2007. Reperfusion injury salvage kinase signalling: taking a RISK for cardioprotection. Heart Fail Rev 12:217–234.

76. Skyschally A, Gres P, Hoffmann S, Haude M, Erbel R, et al. 2007. Bidirectional role of tumor necrosis factor-alpha in coronary microembolization: progressive contractile dysfunction versus delayed protection against infarction. Circ Res 100:140–146.

77. Dettbarn CA, Betto R, Salviati G, Palade P, Jenkins GM, Sabbadini RA. 1994. Modulation of cardiac sarcoplasmic reticulum ryanodine receptor by sphingosine. J Mol Cell Cardiol 26:229–242.

78. Oral H, Dorn GW, 2nd, Mann DL. 1997. Sphingosine mediates the immediate negative inotropic effects of tumor necrosis factor-alpha in the adult mammalian cardiac myocyte. J Biol Chem 272:4836–4842.

79. Thielmann M, Dorge H, Martin C, Belosjorow S, Schwanke U, et al. 2002. Myo-cardial dysfunction with coronary microembolization: signal transduction through a sequence of nitric oxide, tumor necrosis factor-alpha, and sphingosine. Circ Res 90:807–813.

80. Hannun YA, Bell RM. 1989. Functions of sphingolipids and sphingolipid break-down products in cellular regulation. Science 243:500–507.

81. Coroneos E, Martinez M, McKenna S, Kester M. 1995. Differential regulation of sphingomyelinase and ceramidase activities by growth factors and cytokines. Implications for cellular proliferation and differentiation. J Biol Chem 270:23305–23309.

82. Ludwig L, Weihrauch D, Kersten JR, Pagel PS, Warltier DC. 2004. Protein kinase C translocation and Src protein tyrosine kinase activation mediate isoflurane-induced preconditioning in vivo: potential downstream targets of mitochondrial adenosine triphosphate-sensitive potassium channels and reactive oxygen species. Anesthesiology 100:532–539.

83. Kim M, Kim N, D’Agati VD, Emala CW, Sr., Lee HT. 2007. Isoflurane mediates protection from renal ischemia-reperfusion injury via sphingosine kinase and sphingosine-1-phosphate-dependent pathways. Am J Physiol Renal Physiol 293:F1827–F1835.

84. Gray MO, Zhou HZ, Schafhalter-Zoppoth I, Zhu P, Mochly-Rosen D, Messing RO. 2004. Preservation of baseline hemodynamic function and loss of inducible

REfERENCES 307

cardioprotection in adult mice lacking protein kinase C epsilon. J Biol Chem 279:3596–3604.

85. Jin ZQ, Zhou HZ, Zhu P, Honbo N, Mochly-Rosen D, et al. 2002. Cardioprotection mediated by sphingosine-1-phosphate and ganglioside GM-1 in wild-type and PKC epsilon knockout mouse hearts. Am J Physiol Heart Circ Physiol 282:H1970–H1977.

86. Jin ZQ, Karliner JS, Vessey DA. 2008. Ischaemic postconditioning protects iso-lated mouse hearts against ischaemia/reperfusion injury via sphingosine kinase isoform-1 activation. Cardiovasc Res 79:134–140.

87. Zhao ZQ, Corvera JS, Halkos ME, Kerendi F, Wang NP, et al. 2003. Inhibition of myocardial injury by ischemic postconditioning during reperfusion: comparison with ischemic preconditioning. Am J Physiol Heart Circ Physiol 285:H579–H588.

88. Strub GM, Paillard M, Liang J, Gomez L, Allegood JC, et al. 2011. Sphingosine-1-phosphate produced by sphingosine kinase 2 in mitochondria interacts with pro-hibitin 2 to regulate complex IV assembly and respiration. FASEB J 25:600–612.

89. Zhang J, Honbo N, Goetzl EJ, Chatterjee K, Karliner JS, Gray MO. 2007. Signals from type 1 sphingosine 1-phosphate receptors enhance adult mouse cardiac myocyte survival during hypoxia. Am J Physiol Heart Circ Physiol 293:H3150–H3158.

90. Hofmann U, Burkard N, Vogt C, Thoma A, Frantz S, et al. 2009. Protective effects of sphingosine-1-phosphate receptor agonist treatment after myocardial ischaemia-reperfusion. Cardiovasc Res 83:285–293.

91. Means CK, Miyamoto S, Chun J, Brown JH. 2008. S1P1 receptor localization confers selectivity for Gi-mediated cAMP and contractile responses. J Biol Chem 283:11954–11963.

92. Means CK, Xiao CY, Li Z, Zhang T, Omens JH, et al. 2007. Sphingosine 1-phosphate S1P2 and S1P3 receptor-mediated Akt activation protects against in vivo myocar-dial ischemia-reperfusion injury. Am J Physiol Heart Circ Physiol 292:H2944–H2951.

93. Schulz R, Kelm M, Heusch G. 2004. Nitric oxide in myocardial ischemia/reperfusion injury. Cardiovasc Res 61:402–413.

94. Bolli R. 2001. Cardioprotective function of inducible nitric oxide synthase and role of nitric oxide in myocardial ischemia and preconditioning: an overview of a decade of research. J Mol Cell Cardiol 33:1897–1918.

95. Karliner JS, Honbo N, Summers K, Gray MO, Goetzl EJ. 2001. The lysophospho-lipids sphingosine-1-phosphate and lysophosphatidic acid enhance survival during hypoxia in neonatal rat cardiac myocytes. J Mol Cell Cardiol 33:1713–1717.

96. Yeh CC, Li H, Malhotra D, Huang MC, Zhu BQ, et al. 2009. Sphingolipid signaling and treatment during remodeling of the uninfarcted ventricular wall after myo-cardial infarction. Am J Physiol Heart Circ Physiol 296:H1193–H1199.

97. Tsukada YT, Sanna MG, Rosen H, Gottlieb RA. 2007. S1P1-selective agonist SEW2871 exacerbates reperfusion arrhythmias. J Cardiovasc Pharmacol 50:660–669.

98. Hofmann U, Hu K, Walter F, Burkard N, Ertl G, et al. 2010. Pharmacological pre- and post-conditioning with the sphingosine-1-phosphate receptor modulator FTY720 after myocardial ischaemia-reperfusion. Br J Pharmacol 160:1243–1251.


99. Kacimi R, Vessey DA, Honbo N, Karliner JS. 2007. Adult cardiac fibroblasts null for sphingosine kinase-1 exhibit growth dysregulation and an enhanced proin-flammatory response. J Mol Cell Cardiol 43:85–91.

100. Gellings Lowe N, Swaney JS, Moreno KM, Sabbadini RA. 2009. Sphingosine-1-phosphate and sphingosine kinase are critical for transforming growth factor-beta-stimulated collagen production by cardiac fibroblasts. Cardiovasc Res 82:303–312.

101. Lowe NG, Swaney JS, Vekich JA, Patel HH, Roth DM, Sabbadini RA. 2006. S1P-stimulated cardiac fibrosis is attenuated by a novel anti-S1P monoclonal antibody. Abstract 981. Circulation 114:II_179.

102. Salomone S, Potts EM, Tyndall S, Ip PC, Chun J, et al. 2008. Analysis of sphingosine 1-phosphate receptors involved in constriction of isolated cerebral arteries with receptor null mice and pharmacological tools. Br J Pharmacol 153:140–147.

103. Murakami A, Takasugi H, Ohnuma S, Koide Y, Sakurai A, et al. 2010. Sphingosine 1-phosphate (S1P) regulates vascular contraction via S1P3 receptor: investigation based on a new S1P3 receptor antagonist. Mol Pharmacol 77:704–713.

104. Levkau B, Hermann S, Theilmeier G, van der Giet M, Chun J, et al. 2004. High-density lipoprotein stimulates myocardial perfusion in vivo. Circulation 110:3355–3359.

105. Lorenz JN, Arend LJ, Robitz R, Paul RJ, MacLennan AJ. 2007. Vascular dysfunc-tion in S1P2 sphingosine 1-phosphate receptor knockout mice. Am J Physiol Regul Integr Comp Physiol 292:R440–R446.

106. Bolz SS, Vogel L, Sollinger D, Derwand R, Boer C, et al. 2003. Sphingosine kinase modulates microvascular tone and myogenic responses through activation of RhoA/Rho kinase. Circulation 108:342–347.

107. Dantas AP, Igarashi J, Michel T. 2003. Sphingosine 1-phosphate and control of vascular tone. Am J Physiol Heart Circ Physiol 284:H2045–H2052.

108. Igarashi J, Michel T. 2008. S1P and eNOS regulation. Biochim Biophys Acta 1781:489–495.

109. Nofer JR, van der Giet M, Tolle M, Wolinska I, von Wnuck Lipinski K, et al. 2004. HDL induces NO-dependent vasorelaxation via the lysophospholipid receptor S1P3. J Clin Invest 113:569–581.

110. Robert P, Tsui P, Laville MP, Livi GP, Sarau HM, et al. 2001. EDG1 receptor stimulation leads to cardiac hypertrophy in rat neonatal myocytes. J Mol Cell Cardiol 33:1589–1606.

111. Frias MA, James RW, Gerber-Wicht C, Lang U. 2009. Native and reconstituted HDL activate Stat3 in ventricular cardiomyocytes via ERK1/2: role of sphingosine-1-phosphate. Cardiovasc Res 82:313–323.

112. Kunisada K, Tone E, Fujio Y, Matsui H, Yamauchi-Takihara K, Kishimoto T. 1998. Activation of gp130 transduces hypertrophic signals via STAT3 in cardiac myo-cytes. Circulation 98:346–352.

113. Means CK, Brown JH. 2009. Sphingosine-1-phosphate receptor signalling in the heart. Cardiovasc Res 82:193–200.

114. Guo J, MacDonell KL, Giles WR. 1999. Effects of sphingosine 1-phosphate on pacemaker activity in rabbit sino-atrial node cells. Pflugers Arch 438:642–648.

REfERENCES 309

115. Landeen LK, Dederko DA, Kondo CS, Hu BS, Aroonsakool N, et al. 2008. Mecha-nisms of the negative inotropic effects of sphingosine-1-phosphate on adult mouse ventricular myocytes. Am J Physiol Heart Circ Physiol 294:H736–H749.

116. Cohen JA, Chun J. 2011. Mechanisms of fingolimod’s efficacy and adverse effects in multiple sclerosis. Ann Neurol 69:759–777.

117. Sanna MG, Liao J, Jo E, Alfonso C, Ahn MY, et al. 2004. Sphingosine 1-phosphate (S1P) receptor subtypes S1P1 and S1P3, respectively, regulate lymphocyte recir-culation and heart rate. J Biol Chem 279:13839–13848.

118. Budde K, Schmouder RL, Brunkhorst R, Nashan B, Lucker PW, et al. 2002. First human trial of FTY720, a novel immunomodulator, in stable renal transplant patients. J Am Soc Nephrol 13:1073–1083.

119. Forrest M, Sun SY, Hajdu R, Bergstrom J, Card D, et al. 2004. Immune cell regula-tion and cardiovascular effects of sphingosine 1-phosphate receptor agonists in rodents are mediated via distinct receptor subtypes. J Pharmacol Exp Ther 309:758–768.

120. Koyrakh L, Roman MI, Brinkmann V, Wickman K. 2005. The heart rate decrease caused by acute FTY720 administration is mediated by the G protein-gated potas-sium channel I. Am J Transplant 5:529–536.

121. Bolick DT, Srinivasan S, Kim KW, Hatley ME, Clemens JJ, et al. 2005. Sphingosine-1-phosphate prevents tumor necrosis factor-{alpha}-mediated monocyte adhesion to aortic endothelium in mice. Arterioscler Thromb Vasc Biol 25:976–981.

122. Whetzel AM, Bolick DT, Srinivasan S, Macdonald TL, Morris MA, et al. 2006. Sphingosine-1 phosphate prevents monocyte/endothelial interactions in type 1 diabetic NOD mice through activation of the S1P1 receptor. Circ Res 99:731–739.

123. Kimura T, Tomura H, Mogi C, Kuwabara A, Damirin A, et al. 2006. Role of scav-enger receptor class B type I and sphingosine 1-phosphate receptors in high density lipoprotein-induced inhibition of adhesion molecule expression in endo-thelial cells. J Biol Chem 281:37457–37467.

124. Rizza C, Leitinger N, Yue J, Fischer DJ, Wang DA, et al. 1999. Lysophosphatidic acid as a regulator of endothelial/leukocyte interaction. Lab Invest 79:1227–1235.

125. Xia P, Gamble JR, Rye KA, Wang L, Hii CS, et al. 1998. Tumor necrosis factor-alpha induces adhesion molecule expression through the sphingosine kinase pathway. Proc Natl Acad Sci U S A 95:14196–14201.

126. Shimamura K, Takashiro Y, Akiyama N, Hirabayashi T, Murayama T. 2004. Expres-sion of adhesion molecules by sphingosine 1-phosphate and histamine in endo-thelial cells. Eur J Pharmacol 486:141–150.

127. Limaye V, Xia P, Hahn C, Smith M, Vadas MA, et al. 2009. Chronic increases in sphingosine kinase-1 activity induce a pro-inflammatory, pro-angiogenic pheno-type in endothelial cells. Cell Mol Biol Lett 14:424–441.

128. Pettus BJ, Bielawski J, Porcelli AM, Reames DL, Johnson KR, et al. 2003. The sphingosine kinase 1/sphingosine-1-phosphate pathway mediates COX-2 induc-tion and PGE2 production in response to TNF-alpha. FASEB J 17:1411–1421.

129. Sloop CH, Dory L, Roheim PS. 1987. Interstitial fluid lipoproteins. J Lipid Res 28:225–237.


130. Lee JF, Zeng Q, Ozaki H, Wang L, Hand AR, et al. 2006. Dual roles of tight junction-associated protein, zonula occludens-1, in sphingosine 1-phosphate-mediated endothelial chemotaxis and barrier integrity. J Biol Chem 281:29190–29200.

131. Brunham LR, Kruit JK, Iqbal J, Fievet C, Timmins JM, et al. 2006. Intestinal ABCA1 directly contributes to HDL biogenesis in vivo. J Clin Invest 116:1052–1062.

132. Parini P, Johansson L, Broijersen A, Angelin B, Rudling M. 2006. Lipoprotein profiles in plasma and interstitial fluid analyzed with an automated gel-filtration system. Eur J Clin Invest 36:98–104.

133. Pfalzer B, Hamm H, Beisiegel U, Ostendorf P. 1992. Lipoproteins and apolipopro-teins in human pleural effusions. J Lab Clin Med 120:483–493.

134. Vaisar T, Pennathur S, Green PS, Gharib SA, Hoofnagle AN, et al. 2007. Shotgun proteomics implicates protease inhibition and complement activation in the anti-inflammatory properties of HDL. J Clin Invest 117:746–756.

135. Sanchez T, Skoura A, Wu MT, Casserly B, Harrington EO, Hla T. 2007. Induction of vascular permeability by the sphingosine-1-phosphate receptor-2 (S1P2R) and its downstream effectors ROCK and PTEN. Arterioscler Thromb Vasc Biol 27:1312–1318.

136. Camerer E, Regard JB, Cornelissen I, Srinivasan Y, Duong DN, et al. 2009. Sphingosine-1-phosphate in the plasma compartment regulates basal and inflammation-induced vascular leak in mice. J Clin Invest 119:1871–1879.

137. Li X, Stankovic M, Bonder CS, Hahn CN, Parsons M, et al. 2008. Basal and angiopoietin-1-mediated endothelial permeability is regulated by sphingosine kinase-1. Blood 111:3489–3497.

138. Sanna MG, Wang SK, Gonzalez-Cabrera PJ, Don A, Marsolais D, et al. 2006. Enhancement of capillary leakage and restoration of lymphocyte egress by a chiral S1P1 antagonist in vivo. Nat Chem Biol 2:434–441.

139. Foss FW, Jr., Snyder AH, Davis MD, Rouse M, Okusa MD, et al. 2007. Synthesis and biological evaluation of gamma-aminophosphonates as potent, subtype-selective sphingosine 1-phosphate receptor agonists and antagonists. Bioorg Med Chem 15:663–677.

140. McVerry BJ, Garcia JG. 2005. In vitro and in vivo modulation of vascular barrier integrity by sphingosine 1-phosphate: mechanistic insights. Cell Signal 17:131–139.

141. Tauseef M, Kini V, Knezevic N, Brannan M, Ramchandaran R, et al. 2008. Activa-tion of sphingosine kinase-1 reverses the increase in lung vascular permeability through sphingosine-1-phosphate receptor signaling in endothelial cells. Circ Res 103:1164–1172.

142. Feistritzer C, Riewald M. 2005. Endothelial barrier protection by activated protein C through PAR1-dependent sphingosine 1-phosphate receptor-1 crossactivation. Blood 105:3178–3184.

143. Finigan JH, Dudek SM, Singleton PA, Chiang ET, Jacobson JR, et al. 2005. Acti-vated protein C mediates novel lung endothelial barrier enhancement: role of sphingosine 1-phosphate receptor transactivation. J Biol Chem 280:17286–17293.

144. Keul P, Sattler K, Levkau B. 2007. HDL and its sphingosine-1-phosphate content in cardioprotection. Heart Fail Rev 12:301–306.

REfERENCES 311

145. Nofer JR, Bot M, Brodde M, Taylor PJ, Salm P, et al. 2007. FTY720, a synthetic sphingosine 1 phosphate analogue, inhibits development of atherosclerosis in low-density lipoprotein receptor-deficient mice. Circulation 115:501–508.

146. Klingenberg R, Nofer JR, Rudling M, Bea F, Blessing E, et al. 2007. Sphingosine-1-phosphate analogue FTY720 causes lymphocyte redistribution and hypercho-lesterolemia in ApoE-deficient mice. Arterioscler Thromb Vasc Biol 27:2392–2399.

147. Tolle M, Levkau B, Keul P, Brinkmann V, Giebing G, et al. 2005. Immunomodula-tor FTY720 Induces eNOS-dependent arterial vasodilatation via the lysophos-pholipid receptor S1P3. Circ Res 96:913–920.

148. Tolle M, Pawlak A, Schuchardt M, Kawamura A, Tietge UJ, et al. 2008. HDL-associated lysosphingolipids inhibit NAD(P)H oxidase-dependent monocyte che-moattractant protein-1 production. Arterioscler Thromb Vasc Biol 28:1542–1548.

149. Hansson GK, Libby P. 2006. The immune response in atherosclerosis: a double-edged sword. Nat Rev Immunol 6:508–519.

150. Hansson GK, Robertson AK, Soderberg-Naucler C. 2006. Inflammation and ath-erosclerosis. Annu Rev Pathol 1:297–329.

151. Muller H, Hofer S, Kaneider N, Neuwirt H, Mosheimer B, et al. 2005. The immu-nomodulator FTY720 interferes with effector functions of human monocyte-derived dendritic cells. Eur J Immunol 35:533–545.

152. Tacke F, Alvarez D, Kaplan TJ, Jakubzick C, Spanbroek R, et al. 2007. Monocyte subsets differentially employ CCR2, CCR5, and CX3CR1 to accumulate within atherosclerotic plaques. J Clin Invest 117:185–194.

153. Wang F, Okamoto Y, Inoki I, Yoshioka K, Du W, et al. 2010. Sphingosine-1-phos-phate receptor-2 deficiency leads to inhibition of macrophage proinflammatory activities and atherosclerosis in apoE-deficient mice. J Clin Invest 120:3979–3995.

154. Skoura A, Michaud J, Im DS, Thangada S, Xiong Y, et al. 2011. Sphingosine-1-phosphate receptor-2 function in myeloid cells regulates vascular inflammation and atherosclerosis. Arterioscler Thromb Vasc Biol 31:81–85.

155. Keul P, Lucke S, von Wnuck Lipinski K, Bode C, Graler M, et al. 2011. Sphingosine-1-phosphate receptor 3 promotes recruitment of monocyte/macrophages in inflammation and atherosclerosis. Circ Res 108:314–323.

156. Michaud J, Im DS, Hla T. 2010. Inhibitory role of sphingosine 1-phosphate receptor 2 in macrophage recruitment during inflammation. J Immunol 184:1475–1483.

157. Hughes JE, Srinivasan S, Lynch KR, Proia RL, Ferdek P, Hedrick CC. 2008. Sphingosine-1-phosphate induces an anti-inflammatory phenotype in macro-phages. Circ Res 102:950–958.

158. Bornfeldt KE, Graves LM, Raines EW, Igarashi Y, Wayman G, et al. 1995. Sphingosine-1-phosphate inhibits PDGF-induced chemotaxis of human arterial smooth muscle cells: spatial and temporal modulation of PDGF chemotactic signal transduction. J Cell Biol 130:193–206.

159. Okamoto H, Takuwa N, Yokomizo T, Sugimoto N, Sakurada S, et al. 2000. Inhibi-tory regulation of Rac activation, membrane ruffling, and cell migration by the G protein-coupled sphingosine-1-phosphate receptor EDG5 but not EDG1 or EDG3. Mol Cell Biol 20:9247–9261.

160. Shimizu T, Nakazawa T, Cho A, Dastvan F, Shilling D, et al. 2007. Sphingosine 1-phosphate receptor 2 negatively regulates neointimal formation in mouse arter-ies. Circ Res 101:995–1000.


161. Wamhoff BR, Lynch KR, Macdonald TL, Owens GK. 2008. Sphingosine-1- phosphate receptor subtypes differentially regulate smooth muscle cell pheno-type. Arterioscler Thromb Vasc Biol 28:1454–1461.

162. Grabski AD, Shimizu T, Deou J, Mahoney WM, Jr., Reidy MA, Daum G. 2009. Sphingosine-1-phosphate receptor-2 regulates expression of smooth muscle alpha-actin after arterial injury. Arterioscler Thromb Vasc Biol 29:1644–1650.

163. Deutschman DH, Carstens JS, Klepper RL, Smith WS, Page MT, et al. 2003. Pre-dicting obstructive coronary artery disease with serum sphingosine-1-phosphate. Am Heart J 146:62–68.

164. Sattler KJ, Elbasan S, Keul P, Elter-Schulz M, Bode C, et al. 2010. Sphingosine 1-phosphate levels in plasma and HDL are altered in coronary artery disease. Basic Res Cardiol 105:821–832.

165. Yeboah J, McNamara C, Jiang XC, Tabas I, Herrington DM, et al. 2010. Associa-tion of plasma sphingomyelin levels and incident coronary heart disease events in an adult population: multi-ethnic study of atherosclerosis. Arterioscler Thromb Vasc Biol 30:628–633.

166. Kontush A, Chapman MJ. 2006. Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and ath-erosclerosis. Pharmacol Rev 58:342–374.

167. Luke MM, O’Meara ES, Rowland CM, Shiffman D, Bare LA, et al. 2009. Gene variants associated with ischemic stroke: the cardiovascular health study. Stroke 40:363–368.

168. Shiffman D, O’Meara ES, Bare LA, Rowland CM, Louie JZ, et al. 2008. Associa-tion of gene variants with incident myocardial infarction in the Cardiovascular Health Study. Arterioscler Thromb Vasc Biol 28:173–179.

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