Erythrocyte Sphingosine-1-phosphate Research Articles

Beneficial Role of Erythrocyte Sphingosine 1-Phosphate in Preventing Renal Macrophage Polarization and Fibrosis through Combating HIF-1α-Dependent Creatine Phosphate Shuttle

Introduction: Erythrocytes, the major reservoir and supplier for plasma sphingosine 1 phosphate (S1P), is a potent biolipid signaling via its specific receptors responsible for immune cell trafficking and function. Current evidence has revealed that erythrocyte intracellular S1P has its own function to promote oxygen (O 2) delivery to counteract tissue hypoxia. Aim: To understand whether O 2 delivery mediated by erythrocyte S1P is involved in tissue macrophage polarization and fibrosis. Methods and Results: Genetic ablation of erythrocyte SphK1 (the only enzyme to generate S1P in erythrocyte, eSphK1 -/-) resulted in less O 2 delivery from erythrocytes, thus leading to severe renal hypoxia, damage and fibrosis in angiotensin II induced hypertensive kidney disease mouse model. Surprisingly, although plasma S1P level was reduced to 50% in Ang II-infused eSphK1 -/- mice, these mice displayed preferentially elevated pro-fibrosis M2 macrophages surrounding the hypoxic renal tubules. Surprisingly, there was no significant difference of S1P level in either kidney or renal macrophages between Ang II-infused controls and eSphK1 -/- mice, ruling out the possibility of difference of kidney or macrophage S1P levels responsible for renal M2 macrophage polarization. Metabolically, untargeted high-throughput metabolic profiling in macrophages purified from mouse kidney revealed a substantial reduction of amino acids (AAs) and fatty acids (FAs) but increased creatine. We further validate this in vitro by 13C 6, 15N 4-labeled arginine tracer. Hypoxia (1~2% O 2) promoted increased 13C 2-labeled creatine (arginine downstream metabolite) in murine bone marrow derived macrophages (BMDMs) time dependently. At cellular and molecular level, we further demonstrated that hypoxia signaling via HIF-1a directly enhanced IL-4 induced M2 polarization of BMDMs as well as expression of Ckb (a gene encoding creatine shuttle), which can be reversed by Chrysin (an HIF-1α inhibitor). Preclinical studies revealed that chrysin rescued the severe renal damage in eSphK1 -/-mice manipulated with unilateral ureteral obstruction (UUO) and prevented development of chronic kidney disease (CKD) in the control mice. Translational research validated mouse findings in kidney tissue of CKD patients. Conclusion: Our work has revealed that erythrocyte S1P combats HIF1α-dependent creatine shuttle, renal macrophage polarization and fibrosis and highlighted potential diagnostic and therapeutic possibilities for macrophage polarization and renal fibrosis.

Erythrocytes Display Metabolic Changes in High-Altitude Polycythemia.

Qile, Muge, Qiying Xu, Yi Ye, Huifang Liu, Drolma Gomchok, Juanli Liu, Tana Wuren, and Ri-Li Ge. Erythrocytes display metabolic changes in high-altitude polycythemia. High Alt Med Biol. 24:104-109, 2023. Background: Sphingosine-1-phosphate (S1P) levels are increased after acute exposure to high altitude; however, whether this effect is observed in chronic high-altitude hypoxia is unknown. Methods: We studied erythrocyte S1P levels in 13 subjects with high-altitude polycythemia (HAPC) and 13 control subjects and also used a mouse model of HAPC. HAPC subjects lived in Maduo (4,300 m altitude) for 10 years, whereas control subjects lived permanently in Xining (2,260 m). The mouse model of HAPC was established by stimulating an altitude of 5,000 m in a hypobaric chamber for 30 days. Hematology and S1P, CD73, 2,3-bisphosphoglycerate (2,3-BPG), and reticulocyte levels were measured. Results: The hemoglobin concentration and number of red blood cells were significantly elevated in human and mouse HAPC groups. Blood S1P levels in HAPC subjects and mice were higher than those in control groups (p < 0.05 and p < 0.001, respectively). 2,3-BPG and CD73 levels in HAPC subjects were significantly higher than those in control subjects (p < 0.05). No significant changes in reticulocyte levels were observed. Conclusions: The critical altitude-induced metabolic changes such as S1P retained high levels even after prolonged exposure, and it may inspire future research into therapeutic strategies for hypoxia-associated illnesses.

Erythrocyte Sphingosine 1 Phosphate Is Essential to Combat HIF1α-Dependent Creatine Shuttle, Macrophage Polarization and Fibrosis

Erythrocytes have long been considered as the major reservoir and supplier for plasma sphingosine 1 phosphate (S1P), which is a potent biolipid signaling via its specific receptors responsible for immune cell trafficking and polarization of tissue macrophages. Currently, emerging evidence has revealed that erythrocyte intracellular S1P has its own function to promote oxygen (O2) delivery to counteract tissue hypoxia. However, whether O2 delivery mediated by erythrocyte S1P is involved in tissue macrophage polarization, inflammation and fibrosis remains unrecognized. Here we report that genetic ablation of erythrocyte SphK1 (the only enzyme to generate S1P in erythrocyte eSphK1-/-) resulted in less O2 delivery from erythrocytes, thus leading to severe hypoxic tissue microenvironment, kidney damage and fibrosis in a well-accepted pathological hypoxic model infused with angiotensin II (a potent vasoconstrictor known to be elevated in hypertensive patients). Surprisingly, although plasma S1P levels were reduced to 50% in Ang II-infused eSphK1-/- mice, these mice displayed preferentially elevated pro-fibrosis M2 macrophages surrounding the hypoxic renal tubules (one of the most hypoxic sites with Ang II infusion). Metabolically, untargeted high-throughput metabolic profiling in macrophages purified from mouse kidney revealed a substantial reduction of amino acids (AAs) and fatty acids (FAs) but increased creatine. Further studies demonstrated that no significant differences of S1P level in either kidney or renal macrophages between Ang II-infused controls and eSphK1-/- mice, ruling out the possibility of difference of kidney or macrophage S1P levels responsible for renal M2 macrophage polarization in Ang II-infused eSphK1-/- mice. Instead, we revealed that reduced O2 offload from erythrocytes was previously unrecognized but essential to promote tissue M2 polarization and fibrosis by upregulating creatine shuttle to meet rapid intracellular energy needs when FAs, AAs and O2 were insufficient due to hypoxia in Ang II-infused eSphK1-/- mice. At cellular and molecular level, we demonstrated that hypoxia signaling via HIF-1a directly induced M2 polarization as well as expression of Slc6a8 (a gene encoding creatine transport), M2 specific marker gene and fibrotic marker gene in cultured murine BMDMs. Overall, our work has revealed that erythrocyte S1P combats HIF1α-dependent creatine shuttle, tissue macrophage polarization and fibrosis and highlighted potential diagnostic and therapeutic possibilities for macrophage polarization and tissue fibrosis. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Erythrocyte sphingosine kinase regulates intraerythrocytic development of Plasmodium falciparum

The sphingolipid pool is key regulator of vital cellular functions in Plasmodium falciparum a causative agent for deadly malaria. Erythrocytes, the host for asexual stage of Plasmodium, are major reservoir for Sphingosine-1-phosphate (S1P). Erythrocyte possesses Sphingosine kinase (SphK) that catalyzed its biosynthesis from sphingosine (Sph). Since, Plasmodium lacks SphK homologous protein it can be envisaged that it co-opts sphingolipids from both intraerythrocytic as well as extracellular pools for its growth and development. Herein, by sphingosine-NBD probing, we report that infected erythrocytes imports Sph from extracellular pool, which is converted to S1P and thereby taken by P. falciparum. Next, by targeting of the SphK through specific inhibitor N,N-Dimethylsphingosine DMS, we show a reduction in erythrocyte endogenous S1P pool and SphK-phosphorylation that led to inhibition in growth and development of ring stage P. falciparum. Owing to the role of S1P in erythrocyte glycolysis we analyzed uptake of NBD-Glucose and production of lactate in DMS treated and untreated plasmodium. DMS treatment led to decreased glycolysis in Plasmodium. Interestingly the host free Plasmodium did not show any effect on glycolysis with DMS treatment indicating its host-mediated effect. Further to understand the in-vivo anti-plasmodial effects of exogenous and endogenous erythrocyte S1P level, Sphingosine-1-phosphate lyase (S1PL) inhibitor (THI), S1P and SphK-1 inhibitor (DMS), were used in Plasmodium berghei ANKA (PbA) mice model. DMS treatment led to reduction of endogenous S1P conferred significant decrease in parasite load, whereas the plasma level S1P modulated by (THI) and exogenous S1P have no effect on growth of Plasmodium. This suggested erythrocyte endogenous S1P pool is important for Plasmodium growth whereas the plasma level S1P has no effect. Altogether, this study provides insight on cellular processes regulated by S1P in P. falciparum and highlights the novel mechanistically distinct molecular target i.e. SphK-1.

Erythrocyte adaptive metabolic reprogramming under physiological and pathological hypoxia.

The erythrocyte is the most abundant cell type in our body, acting as both a carrier/deliverer and sensor of oxygen (O2). Erythrocyte O2 delivery capacity is finely regulated by sophisticated metabolic control. In recent years, unbiased and robust human metabolomics screening and mouse genetic studies have advanced erythroid research revealing the differential role of erythrocyte hypoxic metabolic reprogramming in normal individuals at high altitudes and patients facing hypoxia, such as sickle cell disease (SCD) and chronic kidney disease (CKD). Here we summarize recent progress and highlight potential therapeutic possibilities. Initial studies showed that elevated soluble CD73 (sCD73, converts AMP to adenosine) results in increased circulating adenosine that activates the A2B adenosine receptor (ADORA2B). Signaling through this axis is co-operatively strengthened by erythrocyte-specific synthesis of sphingosine-1-phosphate (S1P). Ultimately, these mechanisms promote the generation of 2,3-bisphosphoglycerate (2,3-BPG), an erythrocyte-specific allosteric modulator that decreases haemoglobin--O2-binding affinity, and thus, induces deoxygenated sickle Hb (deoxyHbS), deoxyHbS polymerization, sickling, chronic inflammation and tissue damage in SCD. Similar to SCD, plasma adenosine and erythrocyte S1P are elevated in humans ascending to high altitude. At high altitude, these two metabolites are beneficial to induce erythrocyte metabolic reprogramming and the synthesis of 2,3-BPG, and thus, increase O2 delivery to counteract hypoxic tissue damage. Follow-up studies showed that erythrocyte equilibrative nucleoside transporter 1 (eENT1) is a key purinergic cellular component controlling plasma adenosine in humans at high altitude and mice under hypoxia and underlies the quicker and higher elevation of plasma adenosine upon re-ascent because of prior hypoxia-induced degradation of eENT1. More recent studies demonstrated the beneficial role of erythrocyte ADORA2B-mediated 2,3-BPG production in CKD. Taken together, these findings revealed the differential role of erythrocyte hypoxic metabolic reprogramming in normal humans at high altitude and patients with CKD vs. SCD patients and immediately suggest differential and precision therapies to counteract hypoxia among these groups.

Erythrocyte Metabolic Reprogramming by Sphingosine 1-Phosphate in Chronic Kidney Disease and Therapies.

Hypoxia promotes renal damage and progression of chronic kidney disease (CKD). The erythrocyte is the only cell type for oxygen (O2) delivery. Sphingosine 1-phosphate (S1P)-a highly enriched biolipid in erythrocytes-is recently reported to be induced under high altitude in normal humans to enhance O2 delivery. However, nothing is known about erythrocyte S1P in CKD. To investigate the function and metabolic basis of erythrocyte S1P in CKD with a goal to explore potential therapeutics. Using erythrocyte-specific SphK1 (sphingosine kinase 1; the only enzyme to produce S1P in erythrocytes) knockout mice (eSphK1-/-) in an experimental model of hypertensive CKD with Ang II (angiotensin II) infusion, we found severe renal hypoxia, hypertension, proteinuria, and fibrosis in Ang II-infused eSphk1-/- mice compared with controls. Untargeted metabolomics profiling and in vivo U-13C6 isotopically labeled glucose flux analysis revealed that SphK1 is required for channeling glucose metabolism toward glycolysis versus pentose phosphate pathway, resulting in enhanced erythroid-specific Rapoport-Luebering shunt in Ang II-infused mice. Mechanistically, increased erythrocyte S1P functioning intracellularly activates AMPK (AMP-activated protein kinase) 1α and BPGM (bisphosphoglycerate mutase) by reducing ceramide/S1P ratio and inhibiting PP2A (protein phosphatase 2A), leading to increased 2,3-bisphosphoglycerate (an erythrocyte-specific metabolite negatively regulating Hb [hemoglobin]-O2-binding affinity) production and thus more O2 delivery to counteract kidney hypoxia and progression to CKD. Preclinical studies revealed that an AMPK agonist or a PP2A inhibitor rescued the severe CKD phenotype in Ang II-infused eSphK1-/- mice and prevented development of CKD in the control mice by inducing 2,3-bisphosphoglycerate production and thus enhancing renal oxygenation. Translational research validated mouse findings in erythrocytes of hypertensive CKD patients and cultured human erythrocytes. Our study elucidates the beneficial role of eSphk1-S1P in hypertensive CKD by channeling glucose metabolism toward Rapoport-Luebering shunt and inducing 2,3-bisphosphoglycerate production and O2 delivery via a PP2A-AMPK1α signaling pathway. These findings reveal the metabolic and molecular basis of erythrocyte S1P in CKD and new therapeutic avenues.

Mechanism of sphingosine 1-phosphate clearance from blood.

The interplay of sphingosine 1-phosphate (S1P) synthetic and degradative enzymes as well as S1P exporters creates concentration gradients that are a fundamental to S1P biology. Extracellular S1P levels, such as in blood and lymph, are high relative to cellular S1P. The blood-tissue S1P gradient maintains endothelial integrity while local S1P gradients influence immune cell positioning. Indeed, the importance of S1P gradients was recognized initially when the mechanism of action of an S1P receptor agonist used as a medicine for multiple sclerosis was revealed to be inhibition of T-lymphocytes’ recognition of the high S1P in efferent lymph. Furthermore, the increase in erythrocyte S1P in response to hypoxia influences oxygen delivery during high altitude acclimatization. However, understanding of how S1P gradients are maintained is incomplete. For example, S1P is synthesized but is only slowly metabolized by blood yet circulating S1P turns over quickly by an unknown mechanism. Prompted by the counterintuitive observation that blood S1P increases markedly in response to inhibition S1P synthesis (by sphingosine kinase 2 (SphK2)), we studied mice wherein several tissues were made deficient in either SphK2 or S1P degrading enzymes. Our data reveal a mechanism whereby S1P is de-phosphorylated at the hepatocyte surface and the resulting sphingosine is sequestered by SphK phosphorylation and in turn degraded by intracellular S1P lyase. Thus, we identify the liver as the primary site of blood S1P clearance and provide an explanation for the role of SphK2 in this process. Our discovery suggests a general mechanism whereby S1P gradients are shaped.

Reduction of Sphingosine Kinase 1 Phosphorylation and Activity in Plasmodium-Infected Erythrocytes.

Sphingosine-1-phosphate (S1P), a bioactive lipid mediator is involved in an array of biological processes and linked to pathological manifestations. Erythrocyte is known as the major reservoir for S1P as they lack S1P-degrading enzymes (S1P lyase and S1P phosphohydrolase) and harbor sphingosine kinase-1 (SphK-1) essential for sphingosine conversion to S1P. Reduced S1P concentration in serum was correlated with disease severity in patients with Plasmodium falciparum and Plasmodium vivax infections. Herein, we aimed to identify the underlying mechanism and contribution of host erythrocytes toward depleted S1P levels in Plasmodium-infected patients vs. healthy individuals. The level and activity of SphK-1 were measured in vitro in both uninfected and cultured P. falciparum-infected erythrocytes. Infected erythrocytes demonstrated a significant decrease in SphK-1 level in a time-dependent manner. We found that 10–42 h post invasion (hpi), SphK1 level was predominantly reduced to ∼50% in rings, trophozoites, and schizonts compared to uninfected erythrocytes. We next analyzed the phosphorylation status of SphK-1, a modification responsible for its activity and S1P production, in both uninfected control and Plasmodium-infected erythrocytes. Almost ∼50% decrease in phosphorylation of SphK-1 was observed that could be corroborated with significant reduction in the production and release of S1P in infected erythrocytes. Serum S1P levels were studied in parallel in P. falciparum (N = 15), P. vivax (N = 36)-infected patients, and healthy controls (N = 6). The findings revealed that S1P concentration was significantly depleted in uncomplicated malaria cases and was found to be lowest in complicated malaria and thrombocytopenia in both P. falciparum and P. vivax-infected groups (∗∗p < 0.01). The lower serum S1P level could be correlated with the reduced platelet count defining the role of S1P level in platelet formation. In conclusion, erythrocyte SphK-1 and S1P levels were studied in Plasmodium-infected individuals and erythrocytes that helped in characterizing the complications associated with malaria and thrombocytopenia, providing insights into the contribution of host erythrocyte biology in malaria pathogenesis. Finally, this study proposes the use of S1P and its analog as a novel adjunct therapy for malaria complications.

Structural and Functional Insight of Sphingosine 1-Phosphate-Mediated Pathogenic Metabolic Reprogramming in Sickle Cell Disease

Elevated sphingosine 1-phosphate (S1P) is detrimental in Sickle Cell Disease (SCD), but the mechanistic basis remains obscure. Here, we report that increased erythrocyte S1P binds to deoxygenated sickle Hb (deoxyHbS), facilitates deoxyHbS anchoring to the membrane, induces release of membrane-bound glycolytic enzymes and in turn switches glucose flux towards glycolysis relative to the pentose phosphate pathway (PPP). Suppressed PPP causes compromised glutathione homeostasis and increased oxidative stress, while enhanced glycolysis induces production of 2,3-bisphosphoglycerate (2,3-BPG) and thus increases deoxyHbS polymerization, sickling, hemolysis and disease progression. Functional studies revealed that S1P and 2,3-BPG work synergistically to decrease both HbA and HbS oxygen binding affinity. The crystal structure at 1.9 Å resolution deciphered that S1P binds to the surface of 2,3-BPG-deoxyHbA and causes additional conformation changes to the T-state Hb. Phosphate moiety of the surface bound S1P engages in a highly positive region close to α1-heme while its aliphatic chain snakes along a shallow cavity making hydrophobic interactions in the “switch region”, as well as with α2-heme like a molecular “sticky tape” with the last 3–4 carbon atoms sticking out into bulk solvent. Altogether, our findings provide functional and structural bases underlying S1P-mediated pathogenic metabolic reprogramming in SCD and novel therapeutic avenues.

A Rapid Fluorescence Assay for Measuring Sphingosine-1-Phosphate Transporter Activity in Erythrocytes.

Sphingosine-1-phosphate (S1P) is an intercellular signaling molecule that is present in the plasma and plays an important role in recruiting lymphocytes from the thymus and secondary lymphoid organs. Erythrocytes are the most abundant cells in the blood and substantially contribute to the S1P supply in the plasma by releasing intracellularly synthesized S1P via an S1P transporter. Thus, the S1P transporter in erythrocytes is a potential target for immuno-suppressing drugs.In this chapter, we describe a rapid method for measuring the activity of the erythrocyte S1P transporter by using the fluorescent S1P analog, 7-nitro-2-1,3-benzoxadiazol-4-yl (NBD)-labeled S1P. This method does not require chromatography performed with high-performance liquid chromatography, liquid chromatography-tandem mass spectrometry, or thin-layer chromatography methods. Furthermore, S1P transporter activity can be detected by measuring the increase in fluorescence intensity in the extracellular buffer without performing lipid extraction.

Structural and Functional Insight of Sphingosine 1-Phosphate-Mediated Pathogenic Metabolic Reprogramming in Sickle Cell Disease

Sphingosine 1-phosphate (S1P) is a bioactive signaling lipid highly enriched in mature erythrocytes. Previous study has revealed that levels of S1P are significantly elevated in patients and mice with Sickle Cell Disease (SCD), a devastating and highly prevalent genetic hemolytic disorder that causes life-threatening hemolysis, tissue damage, and organ dysfunction with very limited treatment. Moreover, the activity of S1P generating enzyme-Sphingosine Kinase 1 (SphK1) is increased in human and mouse SCD erythrocytes, and inhibition of SphK1 decreased erythrocyte sickling. However, the structural and functional basis for the pathogenic nature of S1P in SCD remains obscure. Here, we report that increased erythrocyte S1P promotes pathogenic metabolic reprogramming coupled to increased channeling of glucose to glycolysis rather than through the pentose phosphate pathway (PPP). Suppressed PPP causes compromised glutathione homeostasis and increased oxidative stress, while enhanced glycolysis induces production of 2,3-bisphosphoglycerate (2,3-BPG) and thus increasing deoxygenated sickle Hb (deoxyHbS), deoxyHbS polymerization, sickling, hemolysis and disease progression. S1P functioning intracellularly binds to deoxyHbS, facilitates deoxyHbS anchoring to the membrane, induces release of membrane-bound glycolytic enzymes and in turn switches glucose flux towards glycolysis relative to the PPP. Extending from SCD, we unexpectedly found that S1P and 2,3-BPG work synergistically to decrease both HbA and HbS oxygen binding affinity. The crystal structure of HbA complexed with S1P alone or in combination with 2,3-BPG at 1.9 Å resolution revealed the overall architecture and unique features of S1P-2,3-BPG-deoxyHbA complex. In the presence of 2,3-BPG, S1P binds to the surface of 2,3-BPG-deoxyHbA and causes additional conformation changes to the T-state Hb. Phosphate moiety of the surface bound S1P engages in a highly positive region close to a1-heme while its aliphatic chain snakes along a shallow cavity making hydrophobic interactions in the "switch region", as well as with b2-heme like a molecular "sticky tape" with the last 3-4 carbon atoms sticking out into bulk solvent. Altogether, our findings provide functional and structural bases underlying pathogenic consequences of elevated S1P in SCD and its potential role in normal erythrocyte physiology. DisclosuresKato:Mast Therapeutics: Consultancy; Bayer: Research Funding.

Fluorescence-based rapid measurement of sphingosine-1-phosphate transport activity in erythrocytes

Sphingosine-1-phosphate (S1P) is present in the blood plasma and acts as a pivotal intercellular signal transmitter in the immune system by recruiting lymphocytes from the thymus and secondary lymphoid tissues. The plasma S1P concentration is maintained by the supply of S1P from erythrocytes. Previously, we showed that S1P release from erythrocytes is mediated by an ATP-dependent transporter. In this study, we attempted to establish a rapid and reliable method for measuring the S1P transport activity in erythrocytes by using a fluorescent S1P analog, 7-nitro-2-1,3-benzoxadiazol-4-yl (NBD)-labeled S1P. NBD-S1P was released from erythrocytes in a time-dependent manner. The NBD-S1P release was reduced after exposure to glyburide, which is an inhibitor of the S1P transporter in erythrocytes. Moreover, the release of NBD-S1P and S1P from erythrocytes was competitively inhibited by intracellular S1P and NBD-S1P, respectively. These results showed that the erythrocyte S1P transporter exports NBD-S1P. We optimized the sample-preparation conditions and lipid extraction to increase the sensitivity of the assay. Furthermore, we successfully measured NBD-S1P release without lipid extraction by decreasing the concentration of BSA in the assay buffer to 0.1%. This method will be useful for the high-throughput screening of S1P transporter inhibitors using conventional fluorometers.

Platelet and Erythrocyte Sources of S1P Are Redundant for Vascular Development and Homeostasis, but Both Rendered Essential After Plasma S1P Depletion in Anaphylactic Shock.

Sphingosine-1-phosphate (S1P) signaling is essential for vascular development and postnatal vascular homeostasis. The relative importance of S1P sources sustaining these processes remains unclear. To address the level of redundancy in bioactive S1P provision to the developing and mature vasculature. S1P production was selectively impaired in mouse platelets, erythrocytes, endothelium, or smooth muscle cells by targeted deletion of genes encoding sphingosine kinases -1 and -2. S1P deficiency impaired aggregation and spreading of washed platelets and profoundly reduced their capacity to promote endothelial barrier function ex vivo. However, and in contrast to recent reports, neither platelets nor any other source of S1P was essential for vascular development, vascular integrity, or hemostasis/thrombosis. Yet rapid and profound depletion of plasma S1P during systemic anaphylaxis rendered both platelet- and erythrocyte-derived S1P essential for survival, with a contribution from blood endothelium observed only in the absence of circulating sources. Recovery was sensitive to aspirin in mice with but not without platelet S1P, suggesting that platelet activation and stimulus-response coupling is needed. S1P deficiency aggravated vasoplegia in this model, arguing a vital role for S1P in maintaining vascular resistance during recovery from circulatory shock. Accordingly, the S1P2 receptor mediated most of the survival benefit of S1P, whereas the endothelial S1P1 receptor was dispensable for survival despite its importance for maintaining vascular integrity. Although source redundancy normally secures essential S1P signaling in developing and mature blood vessels, profound depletion of plasma S1P renders both erythrocyte and platelet S1P pools necessary for recovery and high basal plasma S1P levels protective during anaphylactic shock.

Dose-dependent effect of aspirin on the level of sphingolipids in human blood

Aspirin is an antiplatelet drug which is commonly used in secondary prevention in ischemic heart disease and cerebrovascular events, and in newly diagnosed myocardial infarction. The aim of the present study was to examine effect of aspirin on the level of selected sphingolipid intermediates in plasma, erythrocytes and platelets. Forty two healthy volunteers participated in the study. They were divided into two groups. In one group aspirin was given orally, daily, for one week in a dose of 75 mg (n=25). The subjects from the second group received one 300 mg dose of the drug (n=17). In both groups the blood was taken 4h after the last dose of aspirin. The following sphingolipid intermediates were quantified using high-pressure liquid chromatography: sphinganine, sphingosine, sphingosine-1-phosphate (S1P), sphinganine-1-phosphate (SA1P) and ceramide. It was found that lower dose of aspirin increased the level of S1P and ceramide in erythrocytes (by 23 and 37%, respectively) having no effect on plasma and platelet sphingolipid levels. Higher dose of the drug reduced S1P and SA1P concentration in the plasma (by 16 and 10%, respectively). We conclude that aspirin interferes with sphingolipid metabolism in blood and that this effect depends on a dose of the drug. Since S1P is a potent cardioprotectant, the reduction in its plasma concentration after the loading dose of aspirin could be undesired side effect of the drug.

Role and Regulation Of Erythrocyte Sphingosine Kinase 1 Activity In Normal and Sickle Cell Disease

Sickle Cell Disease (SCD) is a devastating genetic disorder attacking red blood cells (RBCs) and affecting millions of humans worldwide. The Glu/Val mutation in the sixth amino acid of β-globin leads to the polymerization of deoxygenated sickle hemoglobin and subsequent sickling, which initiates the disease. Although SCD has been studied for more than a century, factors that contribute to sickling remain unclear. Our lab recently conducted non-biased metabolomic screening and identified that the levels of a small signaling lipid, sphingosine 1-phosphate (S1P), were dramatically increased in SCD transgenic (Tg) mice and patients. Although S1P is enriched and stored in erythrocytes, the role of S1P in normal and sickle erythrocytes remains unknown. Here we revealed that elevated S1P is a previously unrecognized allosteric modulator collaboratively working with 2, 3-bisiphosphoglycerate (2, 3-BPG) to facilitate oxygen release and thereby triggers sickling. Subsequently, we found that the enzymatic activity of sphingosine kinase 1 (Sphk1), which is the only enzyme producing S1P inside red blood cell (RBCs), is significantly elevated in SCD Tg mice and patients. Intriguingly, we found that hypoxia condition significantly increases Sphk1 activity and decreases hemoglobin oxygen (O2) binding affinity in WT mice but not in Sphk1–deficient mice. In a view of 1) our finding that SphK1 activity is induced by hypoxia; 2) our recent finding that excessive adenosine signaling through the A2B adenosine receptor (ADORA2B) promoting sickling by induction 2,3-BPG (Zhang, et al, Nature Medicine, 2011) and 3) the fact that adenosine is a signaling nucleoside that elicits many physiological effects via its receptors under hypoxic conditions, we hypothesized that adenosine functions via its receptors regulating Sphk1 activity and S1P production in erythrocytes. To test this hypothesis, we conducted both pharmacological and genetic studies. First, we found that adenosine directly induces SphK1 activities in cultured primary mouse and human normal erythrocytes. Next, we found that genetic deletion or inhibition of ADORA2B significantly reduces adenosine-induced SphK1 activities in cultured RBCs. Extending in vitro studies to in vivo experiments, we showed that excess circulating adenosine in adenosine deaminase (ADA, adenosine degrading enzyme)-deficient mice leads to significantly increased erythrocyte SphK1 activities. Similar to in vitro studies, we further found that specific deletion of ADORA2B in ado-/-(i.e ado-/-/adora2b-/- double deficient mice) abolishes excess adenosine-induced SphK1 activities in RBCs. Mechanistically, we further revealed that extralcellular signal regulated kinase (ERK) and protein kinase A (PKA) function downstream of ADORA2B underlying adenosine-induced erythrocyte Sphk1 activity. Overall, our studies demonstrate that 1) S1P is an allosteric modulator to induce O2 release and trigger sickling; 2) elevated adenosine functions via ADORA2B coupled with PKA and ERK signaling network responsible for elevated erythrocyte SphK1 activities and S1P production. Therefore, our findings reveal a previously unrecognized role of SphK1-S1P in erythrocyte physiology and novel mechanisms regulating its activities, add a new insight to the pathophysiology of SCD and open up new therapies for the disease. Disclosures:No relevant conflicts of interest to declare.

Sphingosine 1-Phosphate Receptor Signaling Regulates Proper Embryonic Vascular Patterning

Sphingosine 1-phosphate (S1P) binds G-protein-coupled receptors (S1P(1-5)) to regulate a multitude of physiological effects, especially those in the vascular and immune systems. S1P receptors in the vascular system have been characterized primarily in mammals. Here, we report that the S1P receptors and metabolic enzymes are conserved in the genome of zebrafish Danio rerio. Bioinformatic analysis identified seven S1P receptor-like sequences in the zebrafish genome, including duplicated orthologs of receptors 3 and 5. Sphingolipidomic analysis detected erythrocyte and plasma S1P as well as high plasma ceramides and sphingosine. Morpholino-mediated knockdown of s1pr1 causes global and pericardial edema, loss of blood circulation, and vascular defects characterized by both reduced vascularization in intersegmental vessels, decreased proliferation of intersegmental and axial vessels, and hypersprouting in the caudal vein plexus. The s1pr2 gene was previously characterized as a regulator of cell migration and heart development, but its role in angiogenesis is not known. However, when expression of both s1pr1 and s1pr2 is suppressed, severely reduced vascular development of the intersegmental vessels was observed with doses of the s1pr1 morpholino that alone did not cause any discernible vascular defects, suggesting that s1pr1 and s1pr2 function cooperatively to regulate vascular development in zebrafish. Similarly, the S1P transporter, spns2, also cooperated with s1pr1. We propose that extracellular S1P acts through vascular S1P receptors to regulate vascular development.

Inhibition of Sphk1 Activity in Erythrocytes Ameliorating the Pathophysiology of Sickle Cell Disease

AbstractAbstract 822Sickle cell disease (SCD) is a genetic hemolytic disease with high morbidity and mortality affecting millions of individuals worldwide. Although SCD was identified a century ago, we still lack effective mechanism-based therapies to treat this disease. Using non-biased metabolomic screening, we found that sphingosine-1-phosphate (S1P) is significantly elevated in the blood of SCD mice. Further analysis revealed that the activity of sphingosine kinase 1 (Sphk1, the enzyme that produces S1P) is significantly elevated in erythrocytes of SCD mice. Chronic treatment of SCD mice with a SphK1 inhibitor significantly attenuated sickling, hemolysis, inflammation and multiple tissue damage by reducing erythrocyte and plasma S1P levels. Erythrocyte S1P levels were further elevated following hypoxia/reoxygenation-induced acute sickle crisis (ASC) in SCD mice and blocking its elevation by a Sphk1 specific inhibitor significantly reduced hallmark features associated with ASC and increased survival rates. To extend our pharmacological findings, we utilized a genetic approach to inhibit the synthesis of Sphk1 specifically in hematopoietic cells (HCs). For this purpose we infected bone marrow cells (BMCs) isolated from SCD mice with recombinant lentivirus encoding shRNA specific for Sphk1 or a scrambled shRNA sequence. Following viral transduction, we transplanted the genetically modified BMCs from SCD mice to lethally irradiated WT recipients to generate SCD chimeras. Similarly, we found that knockdown of SphK1 by shRNA in SCD chimeras led to a significant reduction of erythrocyte and plasma S1P and subsequent decreased sickling, hemolysis and inflammatory cells. Strikingly, we found that splenomegaly was substantially reduced in SCD chimera mice with the specific knockdown of SphK1 in hematopoietic cells. As with SCD mice, we found that erythrocyte Sphk1 activity and erythrocyte and plasma S1P levels were significantly elevated in humans with SCD compared to normal individuals. Inhibition of SphK1 in cultured primary human erythrocytes isolated from SCD patients inhibited hypoxia-induced elevation of erythrocyte S1P levels and reduced sickling. Thus, we have revealed for the first time that SphK1-mediated S1P elevation in SCD erythrocytes is a key contributor to sickling in SCD and that Sphk1 inhibition can attenuate both acute and chronic sickling events and disease progression. In an effort to determine the molecular mechanism underlying S1P-induced sickling, we unexpectedly found that S1P directly binds with Hb and results in a reduced Hb-O2 affinity. This finding led us to further discover that 2,3-diphosphoglycerate, another erythrocyte specific allosteric modulator, is required for S1P-mediated allosteric modulation and that these two endogenous heterotropic modulators work cooperatively to induce a substantial reduction in Hb-O2 affinity. Thus, our discovery adds a significant new chapter to erythrocyte physiology by revealing S1P is a novel allosteric modulator of Hb-O2 affinity and also provides a mechanism underlying S1P-mediated sickling by promoting the formation of deoxyHbS. Thus, the work reported here could be the foundation leading to future human trials and a possible therapy for SCD, a life-threatening hemolytic disorder for which the current treatment is extremely limited. Disclosures:No relevant conflicts of interest to declare.

Metabolomic Profiles Reveal Sphingosine-1-Phosphate As a Novel Allosteric Modulator of Hemoglobin-Oxygen Affinity and a Key Contributor to Pathophysiology of Sickle Cell Disease

Abstract LBA-3Sickle cell disease (SCD) is a debilitating hemolytic disorder with high morbidity and mortality affecting millions of individuals worldwide. Although SCD was first identified a century ago, we still lack effective mechanism-based safe therapies to treat this disease. Thus, identification of specific molecules triggering sickling, the central pathogenic process of the disease, is extremely important to advance our understanding of the molecular basis for the pathogenesis of SCD and to develop novel therapeutics.Using non-biased metabolomic screening, we found that sphingosine-1-phosphate (S1P) is significantly elevated in the blood of SCD mice. Further analysis revealed that the activity of sphingosine kinase 1 (Sphk1, the enzyme that produces S1P) is significantly elevated in erythrocytes of SCD mice. Chronic treatment of SCD mice with a SphK1 inhibitor significantly attenuated sickling, hemolysis, inflammation and multiple tissue damage by reducing erythrocyte and plasma S1P levels. Erythrocyte S1P levels were further elevated following hypoxia/reoxygenation-induced acute sickle crisis (ASC) in SCD mice and blocking its elevation by a Sphk1 specific inhibitor significantly reduced hallmark features associated with ASC. As with SCD mice, we found that erythrocyte Sphk1 activity and erythrocyte and plasma S1P levels were significantly elevated in humans with SCD compared to normal individuals. Inhibition of SphK1 in cultured primary human erythrocytes isolated from SCD patients inhibited hypoxia-induced elevation of erythrocyte S1P levels and reduced sickling. Thus, we have revealed for the first time that SphK1-mediated S1P elevation in SCD erythrocytes is a key contributor to sickling in SCD and that Sphk1 inhibition can attenuate both acute and chronic sickling events and disease progression.S1P is an important signaling molecule regulating diverse biological processes. Although S1P is predominantly produced and stored in RBCs, nothing was known about the physiological role of S1P in normal RBCs or the pathophysiological role of S1P in SCD until we conducted a metabolomic screen. In an effort to determine the molecular mechanism underlying S1P-induced sickling, we unexpectedly found that S1P directly binds with Hb and results in a reduced Hb-O2 affinity. This finding led us to further discover that 2,3-diphosphoglycerate, another erythrocyte specific allosteric modulator, is required for S1P-mediated allosteric modulation and that these two endogenous heterotropic modulators work cooperatively to induce a substantial reduction in Hb-O2 affinity. Supporting the biochemical and functional findings, molecular modeling predicts that S1P binds near the water filled central cavity of HbA at a site that is different from the Hb-2,3-DPG binding site. Thus, our discovery adds a significant new chapter to erythrocyte physiology by revealing S1P is a novel allosteric modulator of Hb-O2 affinity and also providing a mechanism underlying S1P-mediated sickling by promoting the formation of deoxyHbS. Thus, the work reported here could be the foundation leading to future human trials and a possible therapy for SCD, a life-threatening hemolytic disorder for which the current treatment is extremely limited.The significance of our findings extends well beyond SCD. Our findings reveal a previously unrecognized important role for S1P in erythrocyte physiology and indicate a new concept for the regulation of O2 release from Hb under normal and sickle cell disease conditions. For SCD, elevated S1P is detrimental because reduced Hb-O2 affinity leads to more deoxygenation of HbS, increased sickling and subsequent multiple life-threatening complications. However, for normal erythrocytes, elevated S1P is likely beneficial by decreasing Hb-O2 affinity allowing for more O2 release to hypoxic tissues. Thus, for humans with normal Hb, if elevated S1P can induce O2 release to hypoxic tissues it may be a novel therapeutic target for a range of disorders, from chronic heart failure to diabetic retinopathy, traumatic blood loss, pulmonary disease and even cancer. In this way our findings reveal important novel opportunities to treat and prevent not only SCD but also multiple cardiovascular and pulmonary diseases associated with hypoxia. Thus, the impact of our novel finding is significant and enormous. Disclosures:No relevant conflicts of interest to declare.

Metabolomic Profiles Reveal Sphingosine-1-Phosphate As a Novel Allosteric Modulator of Hemoglobin-Oxygen Affinity and a Key Contributor to Pathophysiology of Sickle Cell Disease

Abstract LBA-3 Sickle cell disease (SCD) is a debilitating hemolytic disorder with high morbidity and mortality affecting millions of individuals worldwide. Although SCD was first identified a century ago, we still lack effective mechanism-based safe therapies to treat this disease. Thus, identification of specific molecules triggering sickling, the central pathogenic process of the disease, is extremely important to advance our understanding of the molecular basis for the pathogenesis of SCD and to develop novel therapeutics. Using non-biased metabolomic screening, we found that sphingosine-1-phosphate (S1P) is significantly elevated in the blood of SCD mice. Further analysis revealed that the activity of sphingosine kinase 1 (Sphk1, the enzyme that produces S1P) is significantly elevated in erythrocytes of SCD mice. Chronic treatment of SCD mice with a SphK1 inhibitor significantly attenuated sickling, hemolysis, inflammation and multiple tissue damage by reducing erythrocyte and plasma S1P levels. Erythrocyte S1P levels were further elevated following hypoxia/reoxygenation-induced acute sickle crisis (ASC) in SCD mice and blocking its elevation by a Sphk1 specific inhibitor significantly reduced hallmark features associated with ASC. As with SCD mice, we found that erythrocyte Sphk1 activity and erythrocyte and plasma S1P levels were significantly elevated in humans with SCD compared to normal individuals. Inhibition of SphK1 in cultured primary human erythrocytes isolated from SCD patients inhibited hypoxia-induced elevation of erythrocyte S1P levels and reduced sickling. Thus, we have revealed for the first time that SphK1-mediated S1P elevation in SCD erythrocytes is a key contributor to sickling in SCD and that Sphk1 inhibition can attenuate both acute and chronic sickling events and disease progression. S1P is an important signaling molecule regulating diverse biological processes. Although S1P is predominantly produced and stored in RBCs, nothing was known about the physiological role of S1P in normal RBCs or the pathophysiological role of S1P in SCD until we conducted a metabolomic screen. In an effort to determine the molecular mechanism underlying S1P-induced sickling, we unexpectedly found that S1P directly binds with Hb and results in a reduced Hb-O2 affinity. This finding led us to further discover that 2,3-diphosphoglycerate, another erythrocyte specific allosteric modulator, is required for S1P-mediated allosteric modulation and that these two endogenous heterotropic modulators work cooperatively to induce a substantial reduction in Hb-O2 affinity. Supporting the biochemical and functional findings, molecular modeling predicts that S1P binds near the water filled central cavity of HbA at a site that is different from the Hb-2,3-DPG binding site. Thus, our discovery adds a significant new chapter to erythrocyte physiology by revealing S1P is a novel allosteric modulator of Hb-O2 affinity and also providing a mechanism underlying S1P-mediated sickling by promoting the formation of deoxyHbS. Thus, the work reported here could be the foundation leading to future human trials and a possible therapy for SCD, a life-threatening hemolytic disorder for which the current treatment is extremely limited. The significance of our findings extends well beyond SCD. Our findings reveal a previously unrecognized important role for S1P in erythrocyte physiology and indicate a new concept for the regulation of O2 release from Hb under normal and sickle cell disease conditions. For SCD, elevated S1P is detrimental because reduced Hb-O2 affinity leads to more deoxygenation of HbS, increased sickling and subsequent multiple life-threatening complications. However, for normal erythrocytes, elevated S1P is likely beneficial by decreasing Hb-O2 affinity allowing for more O2 release to hypoxic tissues. Thus, for humans with normal Hb, if elevated S1P can induce O2 release to hypoxic tissues it may be a novel therapeutic target for a range of disorders, from chronic heart failure to diabetic retinopathy, traumatic blood loss, pulmonary disease and even cancer. In this way our findings reveal important novel opportunities to treat and prevent not only SCD but also multiple cardiovascular and pulmonary diseases associated with hypoxia. Thus, the impact of our novel finding is significant and enormous. Disclosures: No relevant conflicts of interest to declare.

Exercise increases plasma levels of sphingoid base‐1 phosphates in humans

In recent years, blood sphingolipids attracted much attention and have been implicated in both pathophysiology and prevention of cardiovascular diseases and insulin resistance. However, factors affecting concentration and metabolism of sphingolipids in blood remain poorly recognized. We have previously found that exercise alters skeletal muscle sphingolipid metabolism. This finding prompted us to examine whether physical activity induces similar effects in blood. Twenty healthy male patients were assigned to either untrained (UT, n = 10) or endurance trained (ET, n = 10) group. The patients performed either a 30 (UT group) or 60 (ET group) min exercise on a cycloergometer at a workload corresponding to 70% of VO(2max) . Blood samples were taken just before exercise, after 30 and 60 (ET group only) min of pedalling and following a 30-min rest. ET patients were characterized by higher basal plasma sphingosine-1-phosphate (S1P) concentration and decreased content of sphingosine, S1P, sphinganine-1-phosphate (SA1P) and ceramide in erythrocytes. In ET group, plasma concentrations of all measured sphingolipids remained stable both during and after exercise. On the other hand, in UT patients, the post-exercise levels of S1P and SA1P were markedly higher compared with the baseline values and this effect was accompanied by decreased erythrocyte ceramide content. It is likely that single bout of exercise and endurance training enhances production and release of S1P by erythrocytes. We speculate that exercise-induced increase in plasma S1P concentration might be one of the mechanisms underlying beneficial effects of physical activity on cardiovascular health and insulin sensitivity.