Sphingosine 1-phosphate in vascular biology: possible therapeutic strategies to control vascular diseases

Sphingosine-1-phosphate Decreases Erythrocyte Dysfunction Induced by β-Amyloid

Amyloid beta peptides (Aβ) have been identified as the main pathogenic agents in Alzheimer's disease (AD). Soluble Aβ oligomers, rather than monomer or insoluble amyloid fibrils, show red blood cell (RBC) membrane-binding capacity and trigger several morphological and functional alterations in RBCs that can result in impaired oxygen transport and delivery. Since bioactive lipids have been recently proposed as potent protective agents against Aβ toxicity, we investigated the role of sphingosine-1-phosphate (S1P) in signaling pathways involved in the mechanism underlying ATP release in Ab-treated RBCs. In RBCs following different treatments, the ATP, 2,3 DPG and cAMP levels and caspase 3 activity were determined by spectrophotometric and immunoassay. S1P rescued the inhibition of ATP release from RBCs triggered by Ab, through a mechanism involving caspase-3 and restoring 2,3 DPG and cAMP levels within the cell. These findings reveal the molecular basis of S1P protection against Aβ in RBCs and suggest new therapeutic avenues in AD.

Sphingosine Increases ATP Release From Red Blood Cells

Background:

RBC plays a pivotal role in oxygen delivery, improving distribution where it needs. When RBC enters a low oxygen area, a mechanism mediated by a signaling pathway releases ATP, responsible for vasodilatation.

Objective:

Clarify the potential role of sphingosine on the release of ATP from RBC.

Methods:

ATP release increases after sphingosine exposure in RBC under low oxygen conditions. ATP release in deoxygenated RBC shows data like that of control RBC: (1) RBC after band 3 modification by 4,4'- diisothio-cyanato-stilbene- 2,2'-disulphonic acid (DIDS); (2) CO-treated RBC.

Unlike phosphofructokinase, adenylate cyclase (AC) activity increases after exposure to sphingosine.

Results:

We show that cAMP synthesis and ATP release are not failed in sphingosine-treated red blood cells in response to incubation with mastoparan 7, forskolin plus 3-isobutyl-1-methyl xanthine, agents that stimulate cAMP synthesis.

Conclusion:

Deoxy-hemoglobin, band 3, and AC are involved in the signaling pathway responsible for ATP released after sphingosine exposure.

Sphingosine Increases ATP Release From Red Blood Cells

Background:

RBC plays a pivotal role in oxygen delivery, improving distribution where it needs. When RBC enters a low oxygen area, a mechanism mediated by a signaling pathway releases ATP, responsible for vasodilatation.

Objective:

Clarify the potential role of sphingosine on the release of ATP from RBC.

Methods:

ATP release increases after sphingosine exposure in RBC under low oxygen conditions. ATP release in deoxygenated RBC shows data like that of control RBC: (1) RBC after band 3 modification by 4,4'- diisothio-cyanato-stilbene- 2,2'-disulphonic acid (DIDS); (2) CO-treated RBC.

Unlike phosphofructokinase, adenylate cyclase (AC) activity increases after exposure to sphingosine.

Results:

We show that cAMP synthesis and ATP release are not failed in sphingosine-treated red blood cells in response to incubation with mastoparan 7, forskolin plus 3-isobutyl-1-methyl xanthine, agents that stimulate cAMP synthesis.

Conclusion:

Deoxy-hemoglobin, band 3, and AC are involved in the signaling pathway responsible for ATP released after sphingosine exposure.

Targeting the SphK-S1P-SIPR Pathway as a Potential Therapeutic Approach for COVID-19

The world is currently experiencing the worst health pandemic since the Spanish flu in 1918-the COVID-19 pandemic-caused by the coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This pandemic is the world's third wake-up call this century. In 2003 and 2012, the world experienced two major coronavirus outbreaks, SARS-CoV-1 and Middle East Respiratory syndrome coronavirus (MERS-CoV), causing major respiratory tract infections. At present, there is neither a vaccine nor a cure for COVID-19. The severe COVID-19 symptoms of hyperinflammation, catastrophic damage to the vascular endothelium, thrombotic complications, septic shock, brain damage, acute disseminated encephalomyelitis (ADEM), and acute neurological and psychiatric complications are unprecedented. Many COVID-19 deaths result from the aftermath of hyperinflammatory complications, also referred to as the "cytokine storm syndrome", endotheliitus and blood clotting, all with the potential to cause multiorgan dysfunction. The sphingolipid rheostat plays integral roles in viral replication, activation/modulation of the immune response, and importantly in maintaining vasculature integrity, with sphingosine 1 phosphate (S1P) and its cognate receptors (SIPRs: G-protein-coupled receptors) being key factors in vascular protection against endotheliitus. Hence, modulation of sphingosine kinase (SphK), S1P, and the S1P receptor pathway may provide significant beneficial effects towards counteracting the life-threatening, acute, and chronic complications associated with SARS-CoV-2 infection. This review provides a comprehensive overview of SARS-CoV-2 infection and disease, prospective vaccines, and current treatments. We then discuss the evidence supporting the targeting of SphK/S1P and S1P receptors in the repertoire of COVID-19 therapies to control viral replication and alleviate the known and emerging acute and chronic symptoms of COVID-19. Three clinical trials using FDA-approved sphingolipid-based drugs being repurposed and evaluated to help in alleviating COVID-19 symptoms are discussed.

Metabonomics analysis of liver in rats administered with chronic low-dose acrylamide

The current study aimed to investigate the hepatotoxicity of rats administered with chronic low-dose acrylamide (AA) by using metabonomics technology on the basis of ultraperformance liquid chromatography-mass spectrometry (UPLC-MS). A total of 40 male Wistar rats were randomly divided into the following four groups: control, low-dose AA (0.2 mg/kg bw, non-carcinogenic end-point based on the induction of morphological nerve changes in rats), middle-dose AA (1 mg/kg bw), and high-dose AA (5 mg/kg bw). The rats continuously received AA by administering it in drinking water daily for 16 weeks. After the treatment, rat livers were collected for metabonomics analysis and histopathology examination. Principal components analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) were used to investigate the metabonomics profile changes in rat liver tissues and screen the potential biomarkers.Fourteen metabolites were identified with significant changes in intensities (increased or decreased compared with the control group) as a result of treatment (p < 0.05 or p < 0.01). These metabolites included tauro-b-muricholic acid, docosapentaenoic acid, sphingosine 1-phosphate, taurodeoxycholic acid, lysoPE(20:5), cervonyl carnitine, linoleyl carnitine, docosahexaenoic acid, lysoPC(20:4), lysoPE(18:3), PA(20:4), stearidonyl carnitine, alpha-linolenic acid, and lysoPA(18:0).Results showed that chronic exposure to AA at NOAEL (0.2 mg/kg bw) exhibited no toxic effect in rat livers at the metabolic level. AA induced oxidative stress to the liver and disrupted lipid metabolism. The results of liver histopathology examination further supported the metabonomic results.

Vascular regeneration in adult mouse cochlea stimulated by VEGF-A165 and driven by NG2-derived cells ex vivo

Can damaged or degenerated vessels be regenerated in the ear? The question is clinically important, as disruption of cochlear blood flow is seen in a wide variety of hearing disorders, including in loud sound-induced hearing loss (endothelial injury), ageing-related hearing loss (lost vascular density), and genetic hearing loss (e.g., Norrie disease: strial avascularization). Progression in cochlear blood flow (CBF) pathology can parallel progression in hair cell and hearing loss. However, neither new vessel growth in the ear, nor the role of angiogenesis in hearing, have been investigated. In this study, we used an established ex vivo tissue explant model in conjunction with a matrigel matrix model to demonstrate for the first time that new vessels can be generated by activating a vascular endothelial growth factor (VEGF-A) signal. Most intriguingly, we found that the pattern of the newly formed vessels resembles the natural 'mesh pattern' of in situ strial vessels, with both lumen and expression of tight junctions. Sphigosine-1-phosphate (S1P) in synergy with VEGF-A control new vessel size and growth. Using transgenic neural/glial antigen 2 (NG2) fluorescent reporter mice, we have furthermore discovered that the progenitors of "de novo" strial vessels are NG2-derived cells. Taken together, our data demonstrates that damaged strial microvessels can be regenerated by reprogramming NG2-derived angiogenic cells. Restoration of the functional vasculature may be critical for recovery of vascular dysfunction related hearing loss.

Regulation of the metabolism of apolipoprotein M and sphingosine 1-phosphate by hepatic PPARγ activity

Apolipoprotein M (apoM) is a carrier and a modulator of sphingosine 1-phosphate (S1P), an important multifunctional bioactive lipid. Since peroxisome proliferator-activated receptor γ (PPARγ) is reportedly associated with the function and metabolism of S1P, we investigated the modulation of apoM/S1P homeostasis by PPARγ. First, we investigated the modulation of apoM and S1P homeostasis by the overexpression or knockdown of PPARγ in HepG2 cells and found that both the overexpression and the knockdown of PPARγ decreased apoM expression and S1P synthesis. When we activated or suppressed the PPARγ more mildly with pioglitazone or GW9662, we found that pioglitazone suppressed apoM expression and S1P synthesis, while GW9662 increased them. Next, we overexpressed PPARγ in mouse liver through adenoviral gene transfer and observed that both the plasma and hepatic apoM levels and the plasma S1P levels decreased, while the hepatic S1P levels increased, in the presence of enhanced sphingosine kinase activity. Treatment with pioglitazone decreased both the plasma and hepatic apoM and S1P levels only in diet-induced obese mice. Moreover, the overexpression of apoM increased, while the knockdown of apoM suppressed PPARγ activities in HepG2 cells. These results suggested that PPARγ regulates the S1P levels by modulating apoM in a bell-shaped manner, with the greatest levels of apoM/S1P observed when PPARγ was mildly expressed and that hepatic apoM/PPARγ axis might maintain the homeostasis of S1P metabolism.

Metabonomic analysis of toxic action of long-term low-level exposure to acrylamide in rat serum

This study assessed the effects of long-term, low-dose acrylamide (AA) administration in rats using ultra-performance liquid chromatography–mass spectrometry. Forty male Wistar rats were randomly divided into the following four groups: control, low-dose AA (0.2 mg/kg BW), middle-dose AA (1 mg/kg BW), and high-dose AA (5 mg/kg BW). AA was administered to rats via drinking water ad libitum. After 16-week treatment, rat serum was collected for metabonomic analysis. Biochemical tests were further conducted to verify metabolic alterations. Eleven metabolites were identified with significant changes in intensities (increased or reduced) as a result of treatment. These metabolites included citric acid, pantothenic acid, isobutyryl-l-carnitine, eicosapentaenoic acid, docosahexaenoic acid, sphingosine 1-phosphate, LysoPC(20:4), LysoPC(22:6), LysoPE(20:3), undecanedioic acid, and dodecanedioic acid. Results indicate that chronic exposure to AA at no observed adverse effect level does not exert a toxic effect on rats at the body metabolism level. AA disturbed the metabolism of lipids and energy, affected the nervous system of rats, and induced oxidative stress and liver dysfunction.

Involvement of Band3 in the efflux of sphingosine 1-phosphate from erythrocytes

Sphingosine 1-phosphate (S1P) is a bioactive lipid mediator that is thought to be involved in various diseases. Although the main source of S1P in the plasma is erythrocytes, how S1P is exported from erythrocytes has not been elucidated. When we differentiated K562 cells into erythroblast-like cells with sodium butyrate, we observed that the efflux of S1P was increased without increased expression of previously proposed S1P transporters, while the expression levels of Band3 were increased. Therefore, in this study, we investigated the involvement of Band 3, the most characteristic membranous transporter for erythrocytes, in S1P efflux, using 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid, disodium salt (H2DIDS), which is an inhibitor of Band3. First, we treated human washed erythrocytes with H₂DIDS and found that H₂DIDS decreased the S1P levels in the supernatant, while it increased the cellular S1P contents. Next, when we injected H₂DIDS into mice, the plasma S1P level was significantly decreased. Finally, when we overexpressed or suppressed Band3 in K562 cells, S1P efflux was enhanced or decreased, respectively, while the overexpression of Band3 in HEK293 cells did not modulate S1P efflux. These results suggested the possible involvement of Band3 in the transport of S1P, a multi-functional bioactive phospholipid, from erythrocytes.

Low sphingosine-1-phosphate plasma levels are predictive for increased mortality in patients with liver cirrhosis

Background & aim

The association of circulating sphingosine-1-phosphate (S1P), a bioactive lipid involved in various cellular processes, and related metabolites such as sphinganine-1-phosphate (SA1P) and sphingosine (SPH) with mortality in patients with end-stage liver disease is investigated in the presented study. S1P as a bioactive lipid mediator, is involved in several cellular processes, however, in end-stage liver disease its role is not understood.

Methods

The study cohort consisted of 95 patients with end-stage liver disease and available information on one-year outcome. The median MELD (Model for end-stage liver disease) score was 12.41 (Range 6.43–39.63). The quantification of sphingolipids in citrated plasma specimen was performed after methanolic protein precipitation followed by hydrophilic interaction liquid chromatography and tandem mass spectrometric detection.

Results

S1P and SA1P displayed significant correlations with the MELD score. Patients with circulating S1P levels below the lowest tertile (110.68 ng/ml) showed the poorest one-year survival rate of only 57.1%, whereas one-year survival rate in patients with S1P plasma levels above 165.67 ng/ml was 93.8%. In a multivariate cox regression analysis including platelet counts, concentrations of hemoglobin and MELD score, S1P remained a significant predictor for three-month and one-year mortality.

Conclusions

Low plasma S1P concentrations are highly significantly associated with prognosis in end-stage liver disease. This association is independent of the stage of liver disease. Further studies should be performed to investigate S1P, its role in the pathophysiology of liver diseases and its potential for therapeutic interventions.

Involvement of CETP (Cholesteryl Ester Transfer Protein) in the Shift of Sphingosine-1-Phosphate Among Lipoproteins and in the Modulation of its Functions

OBJECTIVE

Sphingosine-1-phosphate (S1P) is a vasoprotective lipid mediator. About two thirds of plasma S1P rides on high-density lipoprotein (HDL), and several pleiotropic properties of HDL have been ascribed to S1P. In human subjects, CETP (cholesteryl ester transfer protein) greatly influences HDL quantities. In this study, we attempted to elucidate the roles of CETP in the metabolism of S1P.

APPROACH AND RESULTS

We overexpressed CETP in mice that lacked CETP and found that CETP overexpression decreased the HDL level but failed to modulate the levels of S1P and apolipoprotein M (apoM), a carrier of S1P, in the total plasma. We observed, however, that the distribution of S1P and apoM shifted from HDL to apoB-containing lipoproteins. When we administered C₁₇S1P bound to apoM-containing lipoprotein, C₁₇S1P and apoM were rapidly transferred to apoB-containing lipoproteins in CETP-overexpressing mice. When HDL containing C₁₇S1P was mixed with low-density lipoprotein ex vivo, C₁₇S1P shifted to the low-density lipoprotein fraction independent of the presence of CETP. Concordant with these results, apoM was distributed mainly to the same fraction as apo AI in a CETP-deficient subject, although apoM was also detected in apo AI-poor fractions in a corresponding hypercholesterolemia subject. About the bioactivities of S1P carried on each lipoprotein, S1P riding on apoB-containing lipoproteins induced the phosphorylation of Akt (AKT8 virus oncogene cellular homolog) and eNOS (endothelial nitric oxide synthase) in human umbilical vein endothelial cells, and CETP overexpression increased insulin secretion and sensitivity, which was inhibited by an S1P receptor 1 or 3 antagonist.

CONCLUSIONS

CETP modulates the distribution of S1P among lipoproteins, which affects the bioactivities of S1P.

Resveratrol exerts a biphasic effect on apolipoprotein M

BACKGROUND AND PURPOSE

Resveratrol exerts a range of beneficial actions in several areas of pathophysiology, including vascular biology. Here, we have investigated the effects of resveratrol on apolipoprotein M (apoM), a carrier and modulator of sphingosine 1-phosphate (S1P), a vasoactive lipid mediator.

EXPERIMENTAL APPROACH

We used a hepatoma cell line (HepG2), human primary hepatocytes and C57BL/6 mice. We measured apoM, S1P and related enzymes, LDL receptors and sirtuin1 activity, using Western blotting, RT-PCR and enzyme assays. We also used si-RNA to knock-down sirtuin1 in HepG2 cells.

KEY RESULTS

In cultures of HepG2 cells, resveratrol (1-10 μM) increased intracellular apoM and S1P. High concentrations of resveratrol (100 μM) decreased extracellular (in the culture medium) apoM, whereas moderate concentrations of resveratrol (1-10 μM) increased extracellular apoM. High concentrations of resveratrol also increased LDL receptor expression, while all concentrations of resveratrol activated the histone deacetylase sirtuin1. In cultures of human primary hepatocytes, resveratrol, at all concentrations, increased both intra- and extracellular apoM. When wild-type mice were fed a resveratrol-containing chow (0.3% w/w) for 2 weeks, both the plasma and hepatic apoM and S1P levels were increased. However, the resveratrol diet did not affect hepatic LDL receptor levels in this in vivo study.

CONCLUSIONS AND IMPLICATIONS

Resveratrol increased intra- and extracellular levels of apoM, along with intracellular S1P levels, while a high concentration of resveratrol reduced extracellular apoM. The present findings suggest that resveratrol has novel effects on the metabolic kinetics of S1P, a multi-functional bioactive phospholipid.

Sphingosine-1-Phosphate and Its Receptors: A Mutual Link between Blood Coagulation and Inflammation

Sphingosine-1-phosphate (S1P) is a versatile lipid signaling molecule and key regulator in vascular inflammation. S1P is secreted by platelets, monocytes, and vascular endothelial and smooth muscle cells. It binds specifically to a family of G-protein-coupled receptors, S1P receptors 1 to 5, resulting in downstream signaling and numerous cellular effects. S1P modulates cell proliferation and migration, and mediates proinflammatory responses and apoptosis. In the vascular barrier, S1P regulates permeability and endothelial reactions and recruitment of monocytes and may modulate atherosclerosis. Only recently has S1P emerged as a critical mediator which directly links the coagulation factor system to vascular inflammation. The multifunctional proteases thrombin and FXa regulate local S1P availability and interact with S1P signaling at multiple levels in various vascular cell types. Differential expression patterns and intracellular signaling pathways of each receptor enable S1P to exert its widespread functions. Although a vast amount of information is available about the functions of S1P and its receptors in the regulation of physiological and pathophysiological conditions, S1P-mediated mechanisms in the vasculature remain to be elucidated. This review summarizes recent findings regarding the role of S1P and its receptors in vascular wall and blood cells, which link the coagulation system to inflammatory responses in the vasculature.

Fingolimod-Associated Peripheral Vascular Adverse Effects

Fingolimod is the first oral disease-modifying drug approved for the treatment of multiple sclerosis. The drug is usually well tolerated, and common adverse effects include bradycardia, headache, influenza, diarrhea, back pain, increased liver enzyme levels, and cough. Fingolimod is thought to provide therapeutic benefit by preventing normal lymphocyte egress from lymphoid tissues, thus reducing the infiltration of autoaggressive lymphocytes into the central nervous system. However, because the drug acts on different sphingosine-1-phosphate receptors, it may induce several biological effects by influencing endothelial cell-cell adhesion, angiogenesis, vascular development, and cardiovascular function. We describe a patient with multiple sclerosis who, after 3 weeks of fingolimod administration, developed purplish blotches over the dorsal surface of the distal phalanges of the second and fifth digits and the middle phalanx of the fourth ray, itching, and edema on his left hand, without other evident clinical manifestations. When fingolimod therapy was discontinued, the clinical picture regressed within a few days but reappeared after a rechallenge test. Physicians should be aware of unexpected peripheral vascular adverse effects due to fingolimod use, and patients with vascular-based acropathies should be carefully screened and monitored when taking this drug.

Possible involvement of sphingomyelin in the regulation of the plasma sphingosine 1-phosphate level in human subjects

OBJECTIVES

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid mediator. Although the plasma S1P concentration is reportedly determined by cellular components, including erythrocytes, platelets, and vascular endothelial cells, the possible involvement of other factors, such as serum sphingomyelin (SM) and autotaxin (ATX), remains to be elucidated.

DESIGN AND METHODS

We measured S1P using high-performance liquid chromatography (HPLC), SM and lysophosphatidic acid (LPA) using enzymatic assays, ATX antigen using a two-site enzyme immunoassay, and ATX activity using a lysophospholipase D activity assay. To fractionate the lipoproteins, plasma samples were separated using fast protein liquid chromatography (FPLC) utilizing a Superose 6 column.

RESULTS

The plasma S1P level was positively correlated with the levels of SM and lysophosphatidylcholine, but not with the level of phosphatidylcholine. Although SM was present in the very low-density lipoprotein (VLDL) fraction, neither the plasma S1P level nor the SM level was affected by feeding. The plasma S1P level was negatively correlated with the ATX activity. Although the incubation of 100 μmol/L of sphingosylphosphorylcholine (SPC) with the serum resulted in a significant increase in the S1P level because of the presence of ATX, the physiological concentration of SPC did not mimic this effect.

CONCLUSION

The plasma S1P level was affected by the serum SM level, while the possibility of ATX involvement in the increase in the plasma S1P level was considered to be remote at least in healthy human subjects.

Actin polymerization-enhancing drugs promote ovarian follicle growth mediated by the Hippo signaling effector YAP

Hippo signaling pathway consists of conserved serine/threonine kinases to maintain optimal organ sizes. Studies have demonstrated that fragmentation of murine ovaries increases actin polymerization and disrupts Hippo signaling, leading to nuclear translocation of Hippo signaling effector Yes-associated protein (YAP) in ovarian follicles and follicle growth. For patients with polycystic ovarian syndrome showing follicle arrest, ovarian wedge resection and laser drilling promote follicle growth. Because these damaging procedures likely involve actin polymerization, we tested whether actin polymerization-promoting drugs could promote YAP translocation and stimulate follicle growth. Treatment of murine ovaries with μM Jasplakinolide (JASP), an actin polymerization-promoting cyclic peptide, or sphingosine-1-phosphate (S1P), a follicular fluid constituent known to promote actin polymerization, increased the conversion of globular actin to the filamentous form, followed by increased nuclear YAP and expression of downstream connective tissue growth factor (CCN2). After short-term treatments with JASP or S1P, in vitro cultured and in vivo grafted ovaries showed follicle growth. Furthermore, induction of constitutively active YAP in ovarian grafts of transgenic mice enhanced follicle development, whereas treatment of human ovarian cortices with JASP or S1P increased CCN2 expression. Thus, JASP and S1P stimulate follicle growth and are potential therapeutic agents for treating polycystic ovarian syndrome and other ovarian disorders.

Role of sphingosine-1-phosphate receptor 1 and sphingosine-1-phosphate receptor 2 in hyperglycemia-induced endothelial cell dysfunction

The hyperglycemia-induced production of oxidative stress results in endothelial cell dysfunction. Previous studies have demonstrated that sphingosine-1-phosphate (S1P) regulates an array of biological activities in endothelial cells mediated by sphingosine-1-phosphate receptors (S1PRs). However, the role of S1PR-mediated signaling pathways in hyperglycemia-induced endothelial cell dysfunction is currently unknown. In the present study, we aimed to explore the role of S1PRs in endothelial cell dysfunction. For this purpose, hyperglycemia-induced oxidative stress was examined using human umbilical vein endothelial cells (HUVECs) cultured with either normal (5.6 mM) or high (25 mM) levels of glucose. The levels of reactive oxygen species (ROS) and nitric oxide (NO) were determined by flow cytometric (FCM) analysis and nitrate reductase, respectively. Endothelial morphogenesis assay was performed in three-dimensional Matrigel. The mRNA and protein expression levels of S1PRs in the HUVECs were determined by RT-qPCR and western blot analysis, respectively. In addition, ROS, NO and endothelial morphogenesis assays were conducted using the high glucose-treated endothelial cells transfected with adenoviral vector expressing exogenous S1PR1 gene (pAd-S1PR1) or with adenoviral vector expressing S1PR2-specific shRNA (pAd-shRNA-S1PR2). The expression levels of S1PR1 and S1PR2 in the endothelial cells treated with high levels of glucose decreased and increased, respectively. However, the effects of high levels of glucose on S1PR3 were minimal. In addition, high levels of glucose enhanced ROS generation and markedly reduced NO generation and morphogenetic responses. Nevertheless, all the aforementioned changes were completely reversed by transfection with pAd-S1PR1 or pAd-shRNA-S1PR2, which increased S1PR1 and decreased S1PR2 expression, respectively. It can thus be concluded that S1PR1 and S1PR2 play crucial roles in hyperglycemia-induced endothelial cell dysfunction.

LDL receptor and ApoE are involved in the clearance of ApoM-associated sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) is a vasoactive lipid mediator that is speculated to be involved in various aspects of atherosclerosis. About 70% of circulating plasma S1P is carried on HDL, and several pleiotropic properties of HDL have been ascribed to S1P. In the previous study with human subjects, however, LDL cholesterol or apoB, but not HDL cholesterol or apoA-I, had a significant positive correlation with the plasma S1P level, suggesting that the metabolic pathway for LDL might have some roles in the metabolism of S1P. In this study, we analyzed the association between LDL receptor, an important protein in the clearance of LDL, and circulating S1P. We observed that in LDL receptor-overexpressing mice, the plasma S1P levels as well as apolipoprotein M (apoM), a carrier of S1P, were decreased and that exogenously administered C17S1P bound to apoM-containing lipoproteins was cleared more rapidly. Unlike the situation in wild-type mice, LDL receptor overexpression in apoE-deficient mice did not reduce the plasma S1P or apoM levels, suggesting that apoE might be a ligand for the LDL receptor during the clearance of these factors. The present findings clarify the novel roles of the LDL receptor and apoE in the clearance of S1P, a multifunctional bioactive phospholipid.

Atheroprotective role of high-density lipoprotein (HDL)-associated sphingosine-1-phosphate (S1P)

Numerous epidemiological studies documented an inverse relationship between plasma high-density lipoprotein (HDL) cholesterol levels and the extent of atherosclerotic disease. However, clinical interventions targeting HDL cholesterol failed to show clinical benefits with respect to cardiovascular risk reduction, suggesting that HDL components distinct from cholesterol may account for anti-atherogenic effects attributed to this lipoprotein. Sphingosine-1-phosphate (S1P)-a lysosphingolipid exerting its biological activity via binding to specific G protein-coupled receptors and regulating a wide array of biological responses in a variety of different organs and tissues including the cardiovascular system-has been identified as an integral constituent of HDL particles. In the present review, we discuss current evidence from epidemiological studies, experimental approaches in vitro, and animal models of atherosclerosis, suggesting that S1P contributes to atheroprotective effects exerted by HDL particles.

S1P1 receptor modulation preserves vascular function in mesenteric and coronary arteries after CPB in the rat independent of depletion of lymphocytes

Background

Cardiopulmonary bypass (CPB) may induce systemic inflammation and vascular dysfunction. Sphingosine 1-phosphate (S1P) modulates various vascular and immune responses. Here we explored whether agonists of the S1P receptors, FTY720 and SEW2871 improve vascular reactivity after CPB in the rat.

Methods

Experiments were done in male Wistar rats (total n = 127). Anesthesia was induced by isoflurane (2.5–3%) and maintained by fentanyl and midazolam during CPB. After catheterization of the left femoral artery, carotid artery and the right atrium, normothermic extracorporeal circulation was instituted for 60 minutes. In the first part of the study animals were euthanized after either 1 hour, 1 day, 2 or 5 days of the recovery period. In second part of the study animals were euthanized after 1 day of postoperative period. We evaluated the contractile response to phenylephrine (mesenteric arteries) or to serotonin (coronary artery) and vasodilatory response to acethylcholine (both arteries).

Results

Contractile responses to phenylephrine were reduced at 1 day recovery after CPB and Sham as compared to healthy control animals (Emax, mN: 7.9±1.9, 6.5±1.5, and 11.3±1.3, respectively). Mainly FTY720, but not SEW2871, caused lymphopenia in both Sham and CPB groups. In coronary and mesenteric arteries, both FTY720 and SEW2871 normalized serotonin and phenylephrine-mediated vascular reactivity after CPB (p<0.05) and FTY720 increased relaxation to acetylcholine as compared with untreated rats that underwent CPB.

Conclusion

Pretreatment with FTY720 or SEW2871 preserves vascular function in mesenteric and coronary artery after CPB. Therefore, pharmacological activation of S1P₁ receptors may provide a promising therapeutic intervention to prevent CPB-related vascular dysfunction in patients.

Induction of insulin secretion by apolipoprotein M, a carrier for sphingosine 1-phosphate

BACKGROUNDS

High-density lipoprotein (HDL) has been proposed to enhance β-cell functions. Clinical studies have suggested that apolipoprotein M (apoM), which rides mainly on HDL, is involved in diabetes; however, the underlying mechanism has not yet been elucidated. Recently, apoM was shown to be a carrier for sphingosine 1-phosphate (S1P), a bioactive lipid mediator. In the present study, we investigated the modulation of insulin secretion by apoM through the action of S1P.

METHODS AND RESULTS

We overexpressed apoM in the livers of C57BL6 mice using adenovirus gene transfer and found that the blood glucose levels under ad libitum feeding conditions were lower in the apoM-overexpressing mice. While an insulin tolerance test revealed that insulin sensitivity was not significantly affected, a glucose tolerance test revealed that apoM-overexpressing mice had a better glucose tolerance because of enhanced insulin secretion, a phenomenon that was reversed by treatment with VPC 23019, an antagonist against S1P1 and S1P3 receptor. In vitro experiments with MIN6 cells also revealed that apoM-containing lipoproteins enhanced insulin secretion, which was again inhibited by VPC 23019. ApoM retarded the degradation of S1P, and an increase in Pdx1 expression, the attenuation of endoreticulum stress, and the phosphorylation of Akt, AmpK, and Erk were observed as possible underlying mechanisms for the effect of S1P, maintained at a high concentration by apoM, on the increase in insulin secretion.

CONCLUSIONS

ApoM augmented insulin secretion by maintaining the S1P concentration under both in vivo and in vitro conditions.

Modulation of sphingosine-1-phosphate and apolipoprotein M levels in the plasma, liver and kidneys in streptozotocin-induced diabetic mice

AIMS/INTRODUCTION

Sphingosine-1-phosphate (S1P), a multifunctional bioactive lipid mediator, is involved in various diseases. Apolipoprotein M (ApoM) carries S1P on high-density lipoprotein and modulates S1P metabolism to increase the total S1P mass in the body. Both S1P and ApoM are involved in diabetes.

MATERIALS AND METHODS

The present study examined the modulation of S1P and ApoM levels in the plasma, liver and kidneys in streptozotocin-induced diabetes (STZ) mice, and the effects of insulin on the S1P and ApoM levels in the plasma and liver in STZ mice and normal mice. We also examined the effects of insulin and glucose on the ApoM levels in HepG2 cells.

RESULTS

In STZ mice, both the plasma S1P and ApoM levels were higher than those in control mice. The hepatic S1P and ApoM contents were also elevated. The hepatic S1P and ApoM contents were reduced by insulin treatment, whereas high-dose insulin decreased the plasma S1P and ApoM levels. In mice without streptozotocin treatment, the administration of insulin decreased the plasma S1P and ApoM levels, and the hepatic content of ApoM, whereas the hepatic level of S1P was not altered. Treatment with insulin and incubation under a low glucose level decreased the ApoM levels in HepG2 cells. Regarding the kidney, the renal levels of S1P and ApoM were increased in STZ mice, and insulin treatment partially restored this increment.

CONCLUSIONS

In STZ mice, the levels of S1P and ApoM in the plasma, liver, and kidneys were increased. Insulin treatment somehow reversed this modulation in STZ mice.

Sphingosine-1-phosphate induces differentiation of cultured renal tubular epithelial cells under Rho kinase activation via the S1P2 receptor

BACKGROUND

Sphingosine-1-phosphate (S1P) is reportedly involved in the pathogenesis of kidney disease; however, the precise role played by S1P in renal disorders still remains controversial. Rho kinase plays an important role in the development of diabetic nephropathy by inducing glomerular and tubulointerstitial fibrosis. Rho kinase is known to be stimulated by S1P through its specific receptor, S1P2 receptor (S1P2). Hence, we investigated whether S1P-S1P2 signaling plays a role in the epithelial-mesenchymal transition (EMT) through Rho kinase activation in renal tubules.

METHOD

To characterize the distribution of the S1P2, an immunohistochemical examination of the receptor was performed in the kidney of the non-diabetic and diabetic mice. Next, we examined Rho kinase activity as well as E-cadherin and alpha-smooth muscle actin (α-SMA) expression by real-time RT-PCR and western blotting in cultured rat tubular epithelial cells under S1P stimulation with and without a Rho kinase inhibitor and an S1P2 blocker. In addition, the distribution of E-cadherin and α-SMA was examined by immunocytochemistry.

RESULT

S1P2 was expressed mainly in the renal tubules; expression was intense in collecting ducts and distal tubules compared to other segments. S1P induced activation of Rho kinase through the S1P2, which changed the distribution of E-cadherin and increased the expression of α-SMA.

CONCLUSION

Rho kinase activation by S1P via S1P2 initiated EMT changes in cultured renal tubular cells. Our results suggest that excessive stimulation of S1P might facilitate renal fibrosis via activation of Rho kinase through S1P2.

Novel S1P(1) receptor agonists--part 3: from thiophenes to pyridines

In preceding communications we summarized our medicinal chemistry efforts leading to the identification of potent, selective, and orally active S1P1 agonists such as the thiophene derivative 1. As a continuation of these efforts, we replaced the thiophene in 1 by a 2-, 3-, or 4-pyridine and obtained less lipophilic, potent, and selective S1P1 agonists (e.g., 2) efficiently reducing blood lymphocyte count in the rat. Structural features influencing the compounds' receptor affinity profile and pharmacokinetics are discussed. In addition, the ability to penetrate brain tissue has been studied for several compounds. As a typical example for these pyridine based S1P1 agonists, compound 53 showed EC50 values of 0.6 and 352 nM for the S1P1 and S1P3 receptor, respectively, displayed favorable PK properties, and penetrated well into brain tissue. In the rat, compound 53 maximally reduced the blood lymphocyte count for at least 24 h after oral dosing of 3 mg/kg.

Sphingosine 1-phosphate is a key metabolite linking sphingolipids to glycerophospholipids

The sphingolipid metabolite sphingosine 1-phosphate (S1P) is a well-known lipid mediator. As a lipid mediator, S1P must be present in extracellular space and bind to its cell surface receptors (S1P1-5). However, most S1P, synthesized intracellularly, is metabolized without being released into extracellular space, in other words, without functioning as a lipid mediator in the vast majority of cells except those supplying plasma and lymph S1P such as blood cells and endothelial cells. Instead, intracellular S1P plays an important role as an intermediate of the sole sphingolipid-to-glycerophospholipid metabolic pathway. The degradation of S1P by S1P lyase is the first irreversible reaction (committed step) of this pathway. This metabolic pathway is conserved in eukaryotes from yeast to human, indicating its much older origin than the function of S1P as a lipid mediator, which is found to be present only in vertebrates and chordates. The sphingolipid-to-glycerophospholipid metabolism takes place ubiquitously in mammalian tissues, and its defect causes an aberration of several tissue functions as well as abnormal lipid metabolism. Although this metabolic pathway has been known for over four decades, only recently the precise reactions and enzymes involved in this pathway have been revealed. This review will focus on the recent advances in our understanding of the sphingolipid metabolic pathway via S1P and its physiological and pathological roles. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Liver involvement in sphingosine 1-phosphate dynamism revealed by adenoviral hepatic overexpression of apolipoprotein M

OBJECTIVES

Sphingosine 1-phosphate (S1P) is a vasoprotective lipid mediator that is mainly carried on HDL in the circulation and several anti-atherosclerotic properties of HDL is considered to be ascribed to S1P. Since S1P riding on HDL was recently shown to bind to apolipoprotein M (apoM), which is derived from liver, we analyzed the possible involvement of liver in S1P metabolism.

METHODS AND RESULTS

Using adenoviruses, we overexpressed apoM in HepG2 cells and mice livers and found that both the medium/plasma and cell/liver S1P contents increased. Among lipoprotein subclasses, S1P contents increased mainly in HDL fractions. On the other hand, hepatectomy resulted in the reduction of plasma S1P levels in mice. The incubation of S1P in the conditional medium of apoM-overexpressing HepG2 cells interfered with S1P degradation. Furthermore, adenoviral hepatic overexpression of apoM resulted in increase in the S1P level of plasma but not of blood cells, while combination of hepatic apoM overexpression and intraperitoneal administration of C₁₇-sphingosine resulted in the increase in the C₁₇-S1P level both in livers and in plasma, but again not in blood cells.

CONCLUSIONS

Livers are involved in S1P dynamism, and it was suggested that apoM, produced from livers, increases circulating plasma S1P by augmenting the S1P output from livers and modifies extracellular S1P metabolism.

Sphingosine 1-phosphate release from platelets during clot formation: close correlation between platelet count and serum sphingosine 1-phosphate concentration

Background

Sphingosine 1-phosphate (Sph-1-P), abundantly stored in platelets and released extracellularly upon activation, plays important roles as an extracellular mediator by interacting with specific cell surface receptors, especially in the area of vascular biology and immunology/hematology. Although the plasma Sph-1-P level is reportedly determined by red blood cells (RBCs), but not platelets, this may not be true in cases where the platelets have been substantially activated.

Methods and results

We measured the Sph-1-P and dihydrosphingosine 1-phosphate (DHSph-1-P) levels in serum samples (in which the platelets had been fully activated) from subjects with (n = 21) and without (n = 33) hematological disorders. We found that patients with essential thrombocythemia exhibited higher serum Sph-1-P and DHSph-1-P concentrations. The serum Sph-1-P concentration was closely correlated with the platelet count but was very weakly correlated with the RBC count. Similar results were obtained for DHSph-1-P. The serum Sph-1-P and DHSph-1-P levels were inversely correlated with the level of autotaxin (ATX), a lysophosphatidic acid-producing enzyme. A multiple regression analysis also revealed that the platelet count had the greatest explanatory impact on the serum Sph-1-P level.

Conclusions

Our present results showed close correlations between both the serum Sph-1-P and DHSph-1-P levels and the platelet count (but not the RBC count); these results suggest that high concentrations of these sphingoid base phosphates may be released from platelets and may mediate cross talk between platelet activation and the formation of atherosclerotic lesions.

Mechanistic and pharmacological issues of aspirin as an anticancer agent

Recent findings have shown that aspirin, taken for several years, reduces the long-term risk of some cancers, particularly colorectal cancer. The result that aspirin benefit is detectable at daily low-doses (at least 75mg), the same used for the prevention of cardiovascular disease, positions the antiplatelet action of aspirin at the center of its antitumor efficacy. At low-doses given every 24 h, aspirin is acting by a complete and persistent inhibition of cyclooxygenase (COX)-1 in platelets (in the pre-systemic circulation) while causing a limited and rapidly reversible inhibitory effect on COX-2 and/or COX-1 expressed in nucleated cells. Aspirin has a short half-life in human circulation (approximately 20 min); nucleated cells have the ability to resynthesize the acetylated COX-isozymes within a few hours, while platelets do not. COX-independent mechanisms of aspirin, such as the inhibition of Wnt/ β-catenin and NF-kB signaling and the acetylation of extra-COX proteins, have been suggested to play a role in its chemo-preventive effects, but their relevance remains to be demonstrated in vivo at clinical doses. In conclusion, the results of clinical pharmacology and the analysis of randomized and epidemiological studies suggest that colorectal cancer and atherothrombosis share a common mechanism of disease, i.e. enhanced platelet activation in response to injury at distinct sites.

Optimized protocols to analyze sphingosine-1-phosphate signal transduction pathways during acrosomal exocytosis in human sperm

Regulated secretion is a central issue for the specific function of many cells; for instance, mammalian sperm acrosomal exocytosis is essential for egg fertilization. Sphingosine 1-phosphate is a bioactive sphingolipid that regulates crucial physiological processes. We have recently reported that sphingosine 1-phosphate and sphingosine kinase are involved in a novel signaling pathway leading to acrosomal exocytosis (Suhaiman L et al., J Biol Chem 285:1630-16314, 2010). Acrosomal exocytosis in mammalian sperm is a regulated secretion with unusual characteristics. We therefore employed biochemical functional assays to assess the sphingolipid signaling in both permeabilized and nonpermeabilized sperm. The exocytosis of the acrosomal content is regulated by Ca(2+). During exocytosis, changes in [Ca(2+)]i occur induced by either Ca(2+)-influx or Ca(2+)-mobilization from intracellular stores. By using single cell [Ca(2+)] measurements, we detected intracellular Ca(2+) changes after sphingosine 1-phosphate treatment. Additionally, measuring sphingosine kinase activity, we determined that sphingosine 1-phosphate levels increase after an exocytotic stimulus.This chapter is designed to provide the user with sufficient background to analyze sphingosine 1--phosphate signal transduction pathways during acrosomal exocytosis in human sperm.

Sphingolipid signaling in metabolic disorders

Sphingolipids, ubiquitous membrane lipids in eukaryotes, carry out a myriad of critical cellular functions. The past two decades have seen significant advances in sphingolipid research, and in 2010 a first sphingolipid receptor modulator was employed as a human therapeutic. Furthermore, cellular signaling mechanisms regulated by sphingolipids are being recognized as critical players in metabolic diseases. This review focuses on recent advances in cellular and physiological mechanisms of sphingolipid regulation and how sphingolipid signaling influences metabolic diseases. Progress in this area may contribute to new understanding and therapeutic options in complex diseases such as atherosclerosis, diabetes, metabolic syndromes, and cancer.

Vaccine Development to Treat Alzheimer's Disease Neuropathology in APP/PS1 Transgenic Mice

A novel vaccine addressing the major hallmarks of Alzheimer's disease (AD), senile plaque-like deposits of amyloid beta-protein (Aβ), neurofibrillary tangle-like structures, and glial proinflammatory cytokines, has been developed. The present vaccine takes a new approach to circumvent failures of previous ones tested in mice and humans, including the Elan-Wyeth vaccine (AN1792), which caused massive T-cell activation, resulting in a meningoencephalitis-like reaction. The EB101 vaccine consists of Aβ_1-42 delivered in a novel immunogen-adjuvant composed of liposomes-containing sphingosine-1-phosphate (S1P). EB101 was administered to APPswe/PS1dE9 transgenic mice before and after AD-like pathological symptoms were detectable. Treatment with EB101 results in a marked reduction of Aβ plaque burden, decrease of neurofibrillary tangle-like structure density, and attenuation of astrocytosis. In this transgenic mouse model, EB101 reduces the basal immunological interaction between the T cells and immune activation markers in the affected hippocampal/cortical areas, consistent with decreased amyloidosis-induced inflammation. Therefore, immunization with EB101 prevents and reverses AD-like neuropathology in a significant manner by halting disease progression without developing behavioral spatial deficits in transgenic mice.

Berberine reduces fibronectin expression by suppressing the S1P-S1P2 receptor pathway in experimental diabetic nephropathy models

The accumulation of glomerular extracellular matrix (ECM) is one of the critical pathological characteristics of diabetic renal fibrosis. Fibronectin (FN) is an important constituent of ECM. Our previous studies indicate that the activation of the sphingosine kinase 1 (SphK1)-sphingosine 1- phosphate (S1P) signaling pathway plays a key regulatory role in FN production in glomerular mesangial cells (GMCs) under diabetic condition. Among the five S1P receptors, the activation of S1P2 receptor is the most abundant. Berberine (BBR) treatment also effectively inhibits SphK1 activity and S1P production in the kidneys of diabetic models, thus improving renal injury. Based on these data, we further explored whether BBR could prevent FN production in GMCs under diabetic condition via the S1P2 receptor. Here, we showed that BBR significantly down-regulated the expression of S1P2 receptor in diabetic rat kidneys and GMCs exposed to high glucose (HG) and simultaneously inhibited S1P2 receptor-mediated FN overproduction. Further, BBR also obviously suppressed the activation of NF-κB induced by HG, which was accompanied by reduced S1P2 receptor and FN expression. Taken together, our findings suggest that BBR reduces FN expression by acting on the S1P2 receptor in the mesangium under diabetic condition. The role of BBR in S1P2 receptor expression regulation could closely associate with its inhibitory effect on NF-κB activation.

Sphingosine-1-phosphate antibodies as potential agents in the treatment of cancer and age-related macular degeneration

Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid thought to be dysregulated in a variety of disease conditions. In this review, we discuss the roles of S1P in cancer and in wet age-related macular degeneration. We also explore potential treatment strategies for these disorders, including the utility of anti-S1P antibodies acting as molecular sponges to neutralize dysregulated S1P in relevant tissues.

Sphingosine 1-phosphate regulates matrix metalloproteinase-9 expression and breast cell invasion through S1P3-Gαq coupling

Recent evidence suggests that inflammation is involved in malignant progression of breast cancer. Sphingosine 1-phosphate (S1P), acting on the G-protein-coupled receptors, is known as a potent inflammatory mediator. In this study, the effect of the inflammatory lipid S1P on the regulation of invasive/migratory phenotypes of MCF10A human breast epithelial cells was investigated to elucidate a causal relationship between inflammation and the control of invasiveness of breast cells. We show that S1P causes induction of matrix metalloproteinase-9 (MMP-9) in vitro and in vivo, and thus enhances invasion and migration. We also show that fos plays a crucial role in the transcriptional activation of MMP-9 by S1P. In addition, activation of extracellular-signal-regulated kinases 1 and 2 (ERK1/2), p38 and alpha serine/threonine-protein kinase (Akt) are involved in the process of S1P-mediated induction of MMP-9 expression and invasion. Activation of the S1P receptor S1P₃ and G(αq) are required for S1P-induced invasive/migratory responses, suggesting that the enhancement of S1P-mediated invasiveness is triggered by the specific coupling of S1P₃ to the heterotrimeric G(αq) subunit. Activation of phospholipase C-β₄ and intracellular Ca²⁺ release are required for S1P-induced MMP-9 upregulation. Taken together, this study demonstrated that S1P regulates MMP-9 induction and invasiveness through coupling of S1P₃ and G(αq) in MCF10A cells, thus providing a molecular basis for the crucial role of S1P in promoting breast cell invasion.

Release of sphingosine-1-phosphate from human platelets is dependent on thromboxane formation

BACKGROUND

Platelets release the immune-modulating lipid sphingosine-1-phosphate (S1P). However, the mechanisms of platelet S1P secretion are not fully understood.

OBJECTIVES

The present study investigates the function of thromboxane (TX) for platelet S1P secretion during platelet activation and the consequences for monocyte chemotaxis.

METHODS

S1P was detected using thin-layer chromatography in [(3)H]sphingosine-labeled platelets and by mass spectrometry. Monocyte migration was measured in modified Boyden chamber chemotaxis assays.

RESULTS

Release of S1P from platelets was stimulated with protease-activated receptor-1-activating peptide (PAR-1-AP, 100 μM). Acetylsalicylic acid (ASA) and two structurally unrelated reversible cyclooxygenase inhibitors diclofenac and ibuprofen suppressed S1P release. Oral ASA (500-mg single dose or 100 mg over 3 days) attenuated S1P release from platelets in healthy human volunteers ex vivo. This was paralleled by inhibition of TX formation. S1P release was increased by the TX receptor (TP) agonist U-46619, and inhibited by the TP antagonist ramatroban and by inhibitors of ABC-transport. Furthermore, thrombin-induced release of S1P was attenuated in platelets from TP-deficient mice. Supernatants from PAR-1-AP-stimulated human platelets increased the chemotactic capacity of human peripheral monocytes in a S1P-dependent manner via S1P receptors-1 and -3. These effects were inhibited by ASA-pretreatment of platelets.

CONCLUSIONS

TX synthesis and TP activation mediate S1P release after thrombin receptor activation. Inhibition of this pathway may contribute to the anti-inflammatory actions of ASA, for example by affecting activity of monocytes at sites of vascular injury.

Role of sphingosine 1-phosphate in anti-atherogenic actions of high-density lipoprotein

The reverse cholesterol transport mediated by high-density lipoprotein (HDL) is an important mechanism for maintaining body cholesterol, and hence, the crucial anti-atherogenic action of the lipoprotein. Recent studies, however, have shown that HDL exerts a variety of anti-inflammatory and anti-atherogenic actions independently of cholesterol metabolism. The present review provides an overview of the roles of sphingosine 1-phosphate (S1P)/S1P receptor and apolipoprotein A-I/scavenger receptor class B type I systems in the anti-atherogenic HDL actions. In addition, the physiological significance of the existence of S1P in the HDL particles is discussed.

Role of Rho kinase in sphingosine 1-phosphate-mediated endothelial and smooth muscle cell migration and differentiation

The role of sphingosine 1-phosphate (S1P)-induced Rho kinase (ROCK) activation in the angiogenic responses of pulmonary artery-derived endothelial cells (PAEC) and smooth muscle cells (PASMC) was examined. S1P, a biologically active phospholipid that regulates angiogenesis, promoted PAEC chemotaxis and capillary morphogenesis; furthermore, this activity was unaltered by pretreatment with the pharmacological inhibitor of ROCK, H1152. In contrast, S1P (500 nM) significantly inhibited spontaneous PASMC chemotaxis and differentiation; however, this inhibition was eradicated upon H1152 pretreatment. Similarly, PASMCs transfected with ROCK II siRNA diminished S1P-induced inhibition of the development of multi-cellular structures. Analysis by RT-PCR identified the presence of S1P(1) and S1P(3) receptors on both PAECs and PASMCs, while S1P(2) receptor expression was confined to only PASMCs. Consistent with this observation, the S1P(1) and S1P(3) receptor antagonist, VPC23019, virtually abolished the S1P-initiated PAEC differentiation but did not impede the S1P-induced inhibition of PASMC differentiation. However, the S1P(2) receptor antagonist, JTE013, had no effect on S1P-mediated differentiation of PAECs but abolished the S1P-induced inhibition of PASMC function. Co-cultured endothelial and smooth muscle cells differentiated into "neovascular-like" networks, which were significantly inhibited by S1P. The inhibition of co-culture differentiation in both PAECs and PASMCs was negated by H1152 pretreatment. However, when smooth muscle cells were added to S1P-initiated endothelial cell networks, additional S1P treatment did not inhibit the cellular networks generated by these cells. In conclusion, S1P-induced PAEC angiogenic responses are regulated by S1P(1) and/or S1P(3) receptors independent of Rho kinase activation, whereas S1P(2) receptor-mediated curtailment of PASMC function by S1P.

Sphingosine 1-phosphate and sphingosine kinase are involved in a novel signaling pathway leading to acrosomal exocytosis

Regulated secretion is a central issue for the specific function of many cells; for instance, mammalian sperm acrosomal exocytosis is essential for egg fertilization. Sphingosine 1-phosphate is a bioactive sphingolipid that regulates crucial physiological processes. Here we report that this lipid triggers acrosomal exocytosis in human sperm by a mechanism involving a G(i)-coupled receptor. Real-time imaging showed a remarkable increase of cytosolic calcium upon activation with sphingosine 1-phosphate and pharmacological experiments indicate that the process requires extracellular calcium influx through voltage and store-operated calcium channels and efflux from intracellular stores through inositol 1,4,5-trisphosphate-sensitive calcium channels. Sphingosine 1-phosphate-induced exocytosis requires phospholipase C and protein kinase C activation. We investigated possible sources of the lipid. Western blot indicates that sphingosine kinase 1 is present in spermatozoa. Indirect immunofluorescence showed that phorbol ester, a potent protein kinase C activator that can also trigger acrosomal exocytosis, redistributes sphingosine kinase 1 to the acrosomal region. Functional assays showed that phorbol ester-induced exocytosis depends on the activation of sphingosine kinase 1. Furthermore, incorporation of (32)P to sphingosine demonstrates that cells treated with the phorbol ester increase their sphingosine kinase activity that yields sphingosine 1-phosphate. We present here the first evidence indicating that human spermatozoa produce sphingosine 1-phosphate when challenged with an exocytic stimulus. These observations point to a new role of sphingosine 1-phosphate in a signaling cascade that facilitates acrosome reaction providing some clues about novel lipid molecules involved in exocytosis.

Sphingosine kinase and sphingosine 1-phosphate in cardioprotection

Activation of sphingosine kinase/sphingosine 1-phosphate-mediated signaling has emerged as a critical cardioprotective pathway in response to acute ischemia/reperfusion injury. Application of exogenous sphingosine 1-phosphate (S1P) in cultured cardiac myocytes subjected to hypoxia or treatment of isolated hearts either before ischemia or at the onset of reperfusion (pharmacologic preconditioning or postconditioning) exerts prosurvival effects. Synthetic congeners of S1P mimic these responses. Gene-targeted mice null for the sphingosine kinase 1 isoform whose hearts are subjected to ischemia/reperfusion injury exhibit increased infarct size and respond poorly either to ischemic preconditioning or to ischemic postconditioning. Measurements of cardiac sphingosine kinase activity and S1P parallel these observations. High-density lipoprotein is a major carrier of S1P, and studies of hearts in which selected S1P receptors have been deleted implicate the S1P cargo of high-density lipoprotein in cardioprotection. These observations have considerable relevance for future therapeutic approaches to acute and chronic myocardial injury.

Identification of signaling systems in proliferating and involuting phase infantile hemangiomas by genome-wide transcriptional profiling

Infantile hemangiomas are characterized by rapid capillary growth during the first year of life followed by involution during early childhood. The natural history of these lesions creates a unique opportunity to study the changes in gene expression that occur in the vessels of these tumors as they proliferate and regress. Here we use laser capture microdissection and genome-wide transcriptional profiling of vessels from proliferating and involuting hemangiomas to identify differentially expressed genes. Relative to normal placental vessels, proliferating hemangiomas were characterized by increased expression of genes involved in endothelial-pericyte interactions, such as angiopoietin-2 (ANGPT2), jagged-1 (JAG1), and notch-4 (NOTCH4), as well as genes involved in neural and vascular patterning, such as neuropilin-2 (NETO2), a plexin domain containing receptor (plexinC1), and an ephrin receptor (EPHB3). Insulin-like growth factor binding protein-3 (IGFBP3) was down-regulated in proliferating hemangiomas. Involuting hemangiomas were characterized by the expression of chronic inflammatory mediators, such as the chemokine, stromal cell-derived factor-1 (SDF-1), and factors that may attenuate the angiogenic response, such as a member of the Down syndrome critical region (DSCR) family. The identification of genes differentially expressed in proliferating and involuting hemangiomas in vivo will contribute to our understanding of this vascular lesion, which remains a leading cause of morbidity in newborn children.

Unbalanced expression of sphingosine 1-phosphate receptors in diabetic nephropathy

Sphingosine 1-phosphate (Sph-1-P) regulates vascular homeostasis through its receptors like S1P1 and S1P2. While S1P1 works to protect vasculature, S1P2 works antagonistically against it. Therefore, the balance of S1P1 and S1P2 determines the regulation of vascular permeability. In diabetic nephropathy, one of the typical pathological changes is endothelial injury possibly as a result of changes in vascular permeability. Therefore, we hypothesized that the balance of S1P1 and S1P2 expression becomes inappropriate in glomeruli of diabetic nephropathy. To verify the hypothesis, five SD rats with diabetes induced by streptozotocin injection and six control rats injected with only the vehicle were analyzed one year after injection. The glomeruli of the diabetic rats exhibited endothelial injuries. The analysis by real-time PCR revealed that the ratio of S1P2/S1P1 mRNA in the renal cortex of the diabetic rats was significantly higher than that in the non-diabetic control group. Immunohistochemistry revealed that S1P1 was expressed by endothelial and mesangial cells, while S1P2 was mainly expressed by mesangial cells in glomeruli. Furthermore, the ratio of the staining intensity of S1P2 to that of S1P1 in the glomeruli was significantly higher in the diabetic rats. The number of cells expressing PDGF-B, which enhances S1P2 expression, was also higher in the glomeruli of the diabetic rats than in the controls. In conclusion, Sph-1-P signals are preferentially transmitted through S1P2, rather than S1P1, in the glomeruli of rats with diabetic nephropathy. Such unbalanced delivery of the Sph-1-P signals might be involved in the pathogenesis of endothelial injuries.

Sphingosine kinase regulation and cardioprotection

Activation of sphingosine kinase/sphingosine-1-phosphate (SK/S1P)-mediated signalling has been recognized as critical for cardioprotection in response to acute ischaemia/reperfusion injury. Incubation of S1P with cultured cardiac myocytes subjected to hypoxia or treatment of isolated hearts either before ischaemia or at the onset of reperfusion (pharmacologic pre- or postconditioning) results in reduced myocyte injury. Synthetic agonists active at S1P receptors mimic these responses. Gene-targeted mice null for the SK1 isoform whose hearts are subjected to ischaemia/reperfusion injury exhibit increased infarct size and respond poorly either to ischaemic pre- or postconditioning. Measurements of cardiac SK activity and S1P parallel these observations. Ischaemic postconditioning combined with sphingosine and S1P rescues the heart from prolonged ischaemia. These observations may have considerable relevance for future therapeutic approaches to acute and chronic myocardial injury.