Vascular biology: the role of sphingosine 1-phosphate in both the resting state and inflammation

Ponesimod-Associated Macular Edema: Onset and Resolution

Purpose: To present a patient with cystoid macular edema (CME) associated with ponesimod use and offer suggestions for the management of this condition. Methods: A case report is presented. Results: A 75-year-old woman with relapsing-remitting multiple sclerosis had an unremarkable baseline ophthalmic examination prior to starting ponesimod. At her 9-month follow-up, an examination showed the development of CME in the left eye. The patient's macular edema fully resolved after transitioning off ponesimod to an alternative systemic medication and starting treatment with a topical corticosteroid and nonsteroidal anti-inflammatory drug. Conclusions: To our knowledge, this is the first case report discussing the entity and management of ponesimod-associated macular edema. Ponesimod cessation and concomitant topical therapy can result in successful resolution of macular edema.

Dissecting the Therapeutic Mechanisms of Sphingosine-1-Phosphate Receptor Agonism during Ischaemia and Reperfusion

Sphingosine 1-phosphate (S1P) and S1P receptors (S1PR) regulate many cellular processes, including lymphocyte migration and endothelial barrier function. As neutrophils are major mediators of inflammation, their transendothelial migration may be the target of therapeutic approaches to inflammatory conditions such as ischaemia-reperfusion injury (IRI). The aim of this project was to assess whether these therapeutic effects are mediated by S1P acting on neutrophils directly or indirectly through the endothelial cells. First, our murine model of peritoneum cell recruitment demonstrated the ability of S1P to reduce CXCL8-mediated neutrophil recruitment. Mechanistic in vitro studies revealed that S1P signals in neutrophils mainly through the S1PR1 and 4 receptors and induces phosphorylation of ERK1/2; however, this had no effect on neutrophil transmigration and adhesion. S1P treatment of endothelial cells significantly reduced TNF-α-induced neutrophil adhesion under flow (p < 0.01) and transendothelial migration towards CXCL8 during in vitro chemotaxis assays (p < 0.05). S1PR1 agonist CYM5442 treatment of endothelial cells also reduced neutrophil transmigration (p < 0.01) and endothelial permeability (p < 0.005), as shown using in vitro permeability assays. S1PR3 agonist had no effects on chemotaxis or permeability. In an in vivo mouse model of renal IRI, S1PR agonism with CYM5442 reduced endothelial permeability as shown by reduced Evan's Blue dye extravasation. Western blot was used to assess phosphorylation at different sites on vascular endothelial (VE)-cadherin and showed that CYM5442 reduced VEGF-mediated phosphorylation. Taken together, the results of this study suggest that reductions in neutrophil infiltration during IRI in response to S1P are mediated primarily by S1PR1 signalling on endothelial cells, possibly by altering phosphorylation of VE-cadherin. The results also demonstrate the therapeutic potential of S1PR1 agonist during IRI.

A targeted metabolomics approach for sepsis-induced ARDS and its subphenotypes

BACKGROUND

Acute respiratory distress syndrome (ARDS) is etiologically and clinically a heterogeneous disease. Its diagnostic characteristics and subtype classification, and the application of these features to treatment, have been of considerable interest. Metabolomics is becoming important for identifying ARDS biology and distinguishing its subtypes. This study aimed to identify metabolites that could distinguish sepsis-induced ARDS patients from non-ARDS controls, using a targeted metabolomics approach, and to identify whether sepsis-induced direct and sepsis-induced indirect ARDS are metabolically distinct groups, and if so, confirm their metabolites and associated pathways.

METHODS

This study retrospectively analyzed 54 samples of ARDS patients from a sepsis registry that was prospectively collected from March 2011 to February 2018, along with 30 non-ARDS controls. The cohort was divided into direct and indirect ARDS. Metabolite concentrations of five analyte classes (energy metabolism, free fatty acids, amino acids, phospholipids, sphingolipids) were measured using liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry by targeted metabolomics.

RESULTS

In total, 186 metabolites were detected. Among them, 102 metabolites could differentiate sepsis-induced ARDS patients from the non-ARDS controls, while 14 metabolites could discriminate sepsis-induced ARDS subphenotypes. Using partial least-squares discriminant analysis, we showed that sepsis-induced ARDS patients were metabolically distinct from the non-ARDS controls. The main distinguishing metabolites were lysophosphatidylethanolamine (lysoPE) plasmalogen, PE plasmalogens, and phosphatidylcholines (PCs). Sepsis-induced direct and indirect ARDS were also metabolically distinct subgroups, with differences in lysoPCs. Glycerophospholipid and sphingolipid metabolism were the most significant metabolic pathways involved in sepsis-induced ARDS biology and in sepsis-induced direct/indirect ARDS, respectively.

CONCLUSION

Our study demonstrated a marked difference in metabolic patterns between sepsis-induced ARDS patients and non-ARDS controls, and between sepsis-induced direct and indirect ARDS subpheonotypes. The identified metabolites and pathways can provide clues relevant to the diagnosis and treatment of individuals with ARDS.

Sphingosine kinase activity and sphingosine-1-phosphate in the inflamed human periodontium

OBJECTIVES

This study evaluated changes in the levels of Sphingosine-1-Phosphate (S1P) and Sphingosine Kinase (SPHK) activity in response to non-surgical periodontal treatment in humans.

METHODS

Diseased (n = 65) and healthy sites (n = 72) were screened in 18 patients with localized periodontitis stage II or III. Periodontal clinical parameters were recorded, and the gingival crevicular fluid (GCF) collected at baseline, 30 and 90 days of non-surgical treatment. Internal control sites without attachment loss/bleeding were sampled at baseline and after 90 days of treatment. SPHK activity and S1P levels and SPHK 1/2 isoforms were determined in the GCF at different time points using ELISA.

RESULTS

Non-surgical treatment caused significant improvement in all periodontal clinical parameters (p < 0.01). Activity of SPHK and S1P levels was decreased (p < 0.05) 30 days after treatment and continued up to 90 days (p < 0.01); control sites remained unchanged throughout the study and resembled treated sites at 3 months (p > 0.05). SPHK1 levels presented decrease after periodontal treatment (p < 0.001). SPHK2 levels were lower than SPHK1 (p < 0.001) and remained unchanged.

CONCLUSIONS

S1P levels and SPHK activity decreased within 3 months of non-surgical periodontal treatment, which were correlated with improvements in periodontal parameters. Only SPHK1 levels varied significantly in the states of health and disease.

Sphingosine Kinase 1 Regulates the Pulmonary Vascular Immune Response

The aberrant proliferation of pulmonary artery smooth muscle (PASMCs) cells is a defining characteristic of pulmonary arterial hypertension (PAH) and leads to increased vascular resistance, elevated pulmonary pressure, and right heart failure. The sphingosine kinase 1 (SPHK1)/sphingosine-1 phosphate/sphingosine-1 phosphate receptor 2 pathway promotes vascular remodeling and induces PAH. The aim of this study was to identify genes and cellular processes that are modulated by over-expression of SPHK1 in human PASMCs (hPASMCs). RNA was purified and submitted for RNA sequencing to identify differentially expressed genes. Using a corrected p-value threshold of <0.05, there were 294 genes significantly up-regulated while 179 were significantly down-regulated. Predicted effects of these differentially expressed genes were evaluated using the freeware tool Enrichr to assess general gene set over-representation (enrichment) and ingenuity pathway analysis (IPA™) for upstream regulator predictions. We found a strong change in genes that regulated the cellular immune response. IL6, STAT1, and PARP9 were elevated in response to SPHK1 over-expression in hPASMCs. The gene set enrichment mapped to a few immune-modulatory signaling networks, including IFNG. Furthermore, PARP9 and STAT1 protein were elevated in primary hPASMCs isolated from PAH patients. In conclusion, these data suggest a role of Sphk1 regulates pulmonary vascular immune response in PAH.

Serum sphingosine-1-phosphate levels and Sphingosine-1-Phosphate gene polymorphisms in acute respiratory distress syndrome: a multicenter prospective study

BACKGROUND

Sphingosine-1-phosphate (S1P) is a signaling phospholipid involved in pathophysiologic progression of acute respiratory distress syndrome (ARDS) through its roles in endothelial barrier function and immune modulation. We hypothesized that decreased serum S1P level is associated with the clinical outcomes of ARDS and polymorphisms in the S1P gene are associated with serum S1P levels.

METHODS

This multicenter prospective study includes ARDS patients and healthy blood donors as controls. Serum S1P levels were quantified using enzyme-linked immunosorbent assays. Eight tag single nucleotide polymorphisms (SNPs) in the S1P gene were detected, and their associations with S1P levels were evaluated.

RESULTS

A total of 121 ARDS patients and 100 healthy individuals were enrolled. Serum S1P levels were lower in ARDS patients than in controls (P < 0.001). Decreased S1P levels correlated with more organ dysfunction and higher Acute Physiology and Chronic Health Evaluation II scores. Changes in S1P levels in ARDS patients were associated with the clinical outcomes. The recessive model for SNP rs3743631 suggests that GG homozygote is associate with a higher risk for ARDS. The dominant model for SNP rs907045 suggests that AA or TA genotype might increase the risk for ARDS. In ARDS patients, the rs3743631 GG genotype showed lower S1P levels than those harboring AG and AA genotypes. The serum S1P levels of rs907045 AA or TA genotype patients were lower than those of TT genotype.

CONCLUSIONS

Serum S1P levels are dramatically decreased in ARDS patients. Reduced S1P levels are associated with worse clinical outcomes. There is a significant association between S1P rs3743631, rs907045 polymorphisms and susceptibility of ARDS.

Impact of Phospholipid Transfer Protein in Lipid Metabolism and Cardiovascular Diseases

PLTP plays an important role in lipoprotein metabolism and cardiovascular disease development in humans; however, the mechanisms are still not completely understood. In mouse models, PLTP deficiency reduces cardiovascular disease, while its overexpression induces it. Therefore, we used mouse models to investigate the involved mechanisms. In this chapter, the recent main progresses in the field of PLTP research are summarized, and our focus is on the relationship between PLTP and lipoprotein metabolism, as well as PLTP and cardiovascular diseases.

Predicting response to lisinopril in treating hypertension: a pilot study

INTRODUCTION

Only ~ 50% of hypertensive patients will respond to treatment.

OBJECTIVE

This pilot study aims to identify clinical and metabolite markers that predict response to lisinopril.

METHODS

Hypertensive patients (n = 45) received lisinopril (10 mg) at their baseline visit. Blood pressures were reevaluated one week later. Responders to lisinopril (n = 19) were defined by a 10% decline in systolic blood pressure. Plasma metabolites were evaluated with mass spectrometry.

RESULTS

BMI (p = 0.009), GFR (p = 0.015) and 2-oxoglutarate were included in a logistic regression model to predict response to lisinopril.

CONCLUSIONS

Further validation cohorts are needed to confirm the predictive values of these clinical and metabolic markers.

Expression of sphingosine kinase 1 and sphingosine 1-phosphate receptor 3 in malaria-associated acute lung injury/acute respiratory distress syndrome in a mouse model

This study aimed to investigate the expression of sphingosine kinase 1 (SphK-1) and sphingosine 1-phosphate receptor 3 (S1PR-3) in a mouse model of malaria-associated acute lung injury/acute respiratory distress syndrome (ALI/ARDS). DBA/2 mice were infected with Plasmodium berghei ANKA to generate an experimental model of malaria-associated ALI/ARDS. The infected mice were divided into 2 groups based on the histopathological study of lung tissues: those with and those without ALI/ARDS. The expression of the SphK-1 and S1PR-3 proteins in the lung tissues was investigated using immunohistochemical staining and Western blot analysis. In addition, the S1P level was quantified in plasma and lung tissues using an enzyme-linked immunosorbent assay (ELISA). The results demonstrated that the cellular expression of the SphK-1 and S1PR-3 proteins was significantly upregulated in endothelial cells, alveolar epithelial cells and alveolar macrophages in the lung tissues of malaria-infected mice with ALI/ARDS compared with those in the control groups. The increased expression of the SphK-1 and S1PR-3 proteins was confirmed using Western blot analysis. The concentration of S1P in plasma and lung tissues was significantly decreased in malaria-infected mice with ALI/ARDS compared with non-ALI/ARDS and control mice. Furthermore, increased expression of the SphK-1 and S1PR-3 proteins significantly correlated with lung injury scores and S1P concentrations in malaria-infected mice with ALI/ARDS. These findings highlight increased expression of SphK-1 and S1PR-3 in the lung tissues of malaria-infected mice with ALI/ARDS.

Intravascular Schistosoma mansoni Cleave the Host Immune and Hemostatic Signaling Molecule Sphingosine-1-Phosphate via Tegumental Alkaline Phosphatase

Schistosomes are parasitic flatworms that infect the vasculature of >200 million people around the world. These long-lived parasites do not appear to provoke blood clot formation or obvious inflammation around them in vivo. Proteins expressed at the host-parasite interface (such as Schistosoma mansoni alkaline phosphatase, SmAP) are likely key to these abilities. SmAP is a glycoprotein that hydrolyses the artificial substrate p-nitrophenyl phosphate in a reaction that requires Mg2+ and at an optimal pH of 9. SmAP additionally cleaves the nucleoside monophosphates AMP, CMP, GMP, and TMP, all with a similar Km (~600-650 μM). Living adult worms, incubated in murine plasma for 1 h, alter the plasma metabolome; a decrease in sphingosine-1-phosphate (S1P) is accompanied by an increase in the levels of its component parts-sphingosine and phosphate. To test the hypothesis that schistosomes can hydrolyze S1P (and not merely recruit or activate a host plasma enzyme with this function), living intravascular life-stage parasites were incubated with commercially obtained S1P and cleavage of S1P was detected. Parasites whose SmAP gene was suppressed using RNAi were impaired in their ability to cleave S1P compared to controls. In addition, recombinant SmAP hydrolyzed S1P. Since extracellular S1P plays key roles in controlling inflammation and platelet aggregation, we hypothesize that schistosome SmAP, by degrading S1P, can regulate the level of this bioactive lipid in the environment of the parasites to control these processes in the worm's local environment. This is the first report of any parasite being able to cleave S1P.

Sphingosine 1-Phosphate and Atherosclerosis

Sphingosine 1-phosphate (S1P) is a potent lipid mediator that works on five kinds of S1P receptors located on the cell membrane. In the circulation, S1P is distributed to HDL, followed by albumin. Since S1P and HDL share several bioactivities, S1P is believed to be responsible for the pleiotropic effects of HDL. Plasma S1P levels are reportedly lower in subjects with coronary artery disease, suggesting that S1P might be deeply involved in the pathogenesis of atherosclerosis. In basic experiments, however, S1P appears to possess both pro-atherosclerotic and anti-atherosclerotic properties; for example, S1P possesses anti-apoptosis, anti-inflammation, and vaso-relaxation properties and maintains the barrier function of endothelial cells, while S1P also promotes the egress and activation of lymphocytes and exhibits pro-thrombotic properties. Recently, the mechanism for the biased distribution of S1P on HDL has been elucidated; apolipoprotein M (apoM) carries S1P on HDL. ApoM is also a modulator of S1P, and the metabolism of apoM-containing lipoproteins largely affects the plasma S1P level. Moreover, apoM modulates the biological properties of S1P. S1P bound to albumin exerts both beneficial and harmful effects in the pathogenesis of atherosclerosis, while S1P bound to apoM strengthens anti-atherosclerotic properties and might weaken the pro-atherosclerotic properties of S1P. Although the detailed mechanisms remain to be elucidated, apoM and S1P might be novel targets for the alleviation of atherosclerotic diseases in the future.

Homeostatic migration and distribution of innate immune cells in primary and secondary lymphoid organs with ageing

Ageing of the innate and adaptive immune system, collectively termed immune senescence, is a complex process. One method to understand the components of ageing involves dissociating the effects of ageing on the cells of the immune system, on the microenvironment in lymphoid organs and tissues where immune cells reside and on the circulating factors that interact with both immune cells and their microenvironment. Heterochronic parabiosis, a surgical union of two organisms of disparate ages, is ideal for this type of study, as it has the power to dissociate the age of the cell and the age of the microenvironment into which the cell resides or is migrating. So far, however, it has been used sparingly to study immune ageing. Here we review the limited literature on homeostatic innate immune cell trafficking in ageing in the absence of chronic inflammation. We also review our own recent data on trafficking of innate immune subsets between primary and secondary lymphoid organs in heterochronic parabiosis. We found no systemic bias in retention or acceptance of neutrophils, macrophages, dendritic cells or natural killer cells with ageing in primary and secondary lymphoid organs. We conclude that these four innate immune cell types migrate to and populate lymphoid organs (peripheral lymph nodes, spleen and bone marrow), regardless of their own age and of the age of lymphoid organs.

Therapeutic Strategies and Pharmacological Tools Influencing S1P Signaling and Metabolism

During the last two decades the study of the sphingolipid anabolic, catabolic, and signaling pathways has attracted enormous interest. Especially the introduction of fingolimod into market as first p.o. therapeutic for the treatment of multiple sclerosis has boosted this effect. Although the complex regulation of sphingosine-1-phosphate (S1P) and other catabolic and anabolic sphingosine-related compounds is not fully understood, the influence on different (patho)physiological states from inflammation to cytotoxicity as well as the availability of versatile pharmacological tools that represent new approaches to study these states are described. Here, we have summarized various aspects concerning the many faces of sphingolipid function modulation by different pharmacological tools up to clinical candidates. Due to the immense heterogeneity of physiological or pharmacological actions and complex cross regulations, it is difficult to predict their role in upcoming therapeutic approaches. Currently, inflammatory, immunological, and/or antitumor aspects are discussed.

Sphingosine-1-Phosphate Signaling in Immune Cells and Inflammation: Roles and Therapeutic Potential

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite involved in many critical cell processes. It is produced by the phosphorylation of sphingosine by sphingosine kinases (SphKs) and exported out of cells via transporters such as spinster homolog 2 (Spns2). S1P regulates diverse physiological processes by binding to specific G protein-binding receptors, S1P receptors (S1PRs) 1-5, through a process coined as "inside-out signaling." The S1P concentration gradient between various tissues promotes S1PR1-dependent migration of T cells from secondary lymphoid organs into the lymphatic and blood circulation. S1P suppresses T cell egress from and promotes retention in inflamed peripheral tissues. S1PR1 in T and B cells as well as Spns2 in endothelial cells contributes to lymphocyte trafficking. FTY720 (Fingolimod) is a functional antagonist of S1PRs that induces systemic lymphopenia by suppression of lymphocyte egress from lymphoid organs. In this review, we summarize previous findings and new discoveries about the importance of S1P and S1PR signaling in the recruitment of immune cells and lymphocyte retention in inflamed tissues. We also discuss the role of S1P-S1PR1 axis in inflammatory diseases and wound healing.

A practical process for the preparation of [(32)P]S1P and binding assay for S1P receptor ligands

Sphingosine-1-phosphate receptors (S1PRs) are important regulators of vascular permeability, inflammation, angiogenesis and vascular maturation. Identifying a specific S1PR PET radioligand is imperative, but it is hindered by the complexity and variability of current for binding affinity measurement procedures. Herein, we report a streamlined protocol for radiosynthesis of [(32)P]S1P with good radiochemical yield (36-50%) and high radiochemical purity (>99%). We also report a reproducible procedure for determining the binding affinity for compounds targeting S1PRs in vitro.

Sphingosin-1-phosphate Receptor 1: a Potential Target to Inhibit Neuroinflammation and Restore the Sphingosin-1-phosphate Metabolism

BACKGROUND

Recent evidence suggests that an extreme shift may occur in sphingosine metabolism in neuroinflammatory contexts. Sphingosine 1-phosphate (S1P)-metabolizing enzymes (SMEs) regulate the level of S1P. We recently found that FTY720, a S1P analogue, and SEW2871, a selective S1P receptor 1 (S1P1) agonist, provide protection against neural damage and memory deficit in amyloid beta (Aβ)-injected animals. This study aimed to evaluate the effects of these two analogues on the expression of SMEs as well as their anti-inflammatory roles.

METHODS

Rats were treated with intracerebral lipopolysaccharide (LPS) or Aβ. Memory impairment was assessed by Morris water maze and the effects of drugs on SMEs as well as inflammatory markers, TNF- α and COX-II, were determined by immunoblotting.

RESULTS

Aβ and LPS differentially altered the expression profile of SMEs. In Aβ-injected animals, FTY720 and SEW2871 treatments exerted anti-inflammatory effects and restored the expression profile of SMEs, in parallel to our previous findings. In LPS animals however, in spite of anti-inflammatory effects of the two analogues, only FTY720 restored the levels of SMEs and prevented memory deficit.

CONCLUSION

The observed ameliorating effects of FTY720 and SEW7821 can be partly attributed to the interruption of the vicious cycle of abnormal S1P metabolism and neuro-inflammation. The close imitation of the FTY720 effects by SW2871 in Aβ-induced neuro-inflammation may highlight the attractive role of S1P1 as a potential target to restore S1P metabolism and inhibit inflammatory processes.

Sphingosine kinase 1 deficiency confers protection against hyperoxia-induced bronchopulmonary dysplasia in a murine model: role of S1P signaling and Nox proteins

Bronchopulmonary dysplasia of the premature newborn is characterized by lung injury, resulting in alveolar simplification and reduced pulmonary function. Exposure of neonatal mice to hyperoxia enhanced sphingosine-1-phosphate (S1P) levels in lung tissues; however, the role of increased S1P in the pathobiological characteristics of bronchopulmonary dysplasia has not been investigated. We hypothesized that an altered S1P signaling axis, in part, is responsible for neonatal lung injury leading to bronchopulmonary dysplasia. To validate this hypothesis, newborn wild-type, sphingosine kinase1(-/-) (Sphk1(-/-)), sphingosine kinase 2(-/-) (Sphk2(-/-)), and S1P lyase(+/-) (Sgpl1(+/-)) mice were exposed to hyperoxia (75%) from postnatal day 1 to 7. Sphk1(-/-), but not Sphk2(-/-) or Sgpl1(+/-), mice offered protection against hyperoxia-induced lung injury, with improved alveolarization and alveolar integrity compared with wild type. Furthermore, SphK1 deficiency attenuated hyperoxia-induced accumulation of IL-6 in bronchoalveolar lavage fluids and NADPH oxidase (NOX) 2 and NOX4 protein expression in lung tissue. In vitro experiments using human lung microvascular endothelial cells showed that exogenous S1P stimulated intracellular reactive oxygen species (ROS) generation, whereas SphK1 siRNA, or inhibitor against SphK1, attenuated hyperoxia-induced S1P generation. Knockdown of NOX2 and NOX4, using specific siRNA, reduced both basal and S1P-induced ROS formation. These results suggest an important role for SphK1-mediated S1P signaling-regulated ROS in the development of hyperoxia-induced lung injury in a murine neonatal model of bronchopulmonary dysplasia.

FTY720 prevents progression of renal fibrosis by inhibiting renal microvasculature endothelial dysfunction in a rat model of chronic kidney disease

Recent studies have shown that chronic endothelial dysfunction can impair multiple aspects of renal physiology and, in turn, contribute to renal fibrosis. Sphingosine 1-phosphate (S1P) has been highlighted as an endothelial barrier-stabilizing mediator. The aim of our study was to investigate the effect of FTY720, an S1P analog, on the progression of renal fibrosis by inhibiting renal microvasculature endothelial dysfunction in a rat model of chronic kidney disease. Thirty male Sprague-Dawley rats were used in this study. Seven days after surgery, we placed the animals into three groups: sham surgery; 5/6 nephrectomized (Nx) rats; and 5/6Nx + FTY720 (1 mg/kg/day). All of the animals were sacrificed 12 weeks after surgery. We obtained and analyzed blood and kidney tissue samples from all of the groups. Glomerular capillary density and peritubular capillary (PTC) density were determined by CD31 immunostaining. The expression of transforming growth factor beta 1 (TGF-β1), collagen IV, fibronectin, endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) were analyzed by immunohistochemistry, reverse transcription-polymerase chain reaction and western blotting. The 5/6Nx group exhibited increased blood urea nitrogen and serum creatinine, visible renal histological changes, pro-fibrotic molecule (TGF-β1) and production of extracellular matrix proteins such as collagen IV and fibronectin and decreased glomerular and PTC density, compared to the sham controls (P < 0.01). We observed that treatment with FTY720 reduced these abnormalities. Furthermore, the level of NO, the expression levels of eNOS and VEGF were downregulated in the kidney tissue in 5/6Nx rats, FTY720 treatment significantly attenuated this decrease. FTY720 prevents the progression of renal fibrosis by inhibiting renal microvasculature endothelial dysfunction in a rat model of chronic kidney disease.

Functional promoter variants in sphingosine 1-phosphate receptor 3 associate with susceptibility to sepsis-associated acute respiratory distress syndrome

The genetic mechanisms underlying the susceptibility to acute respiratory distress syndrome (ARDS) are poorly understood. We previously demonstrated that sphingosine 1-phosphate (S1P) and the S1P receptor S1PR3 are intimately involved in lung inflammatory responses and vascular barrier regulation. Furthermore, plasma S1PR3 protein levels were shown to serve as a biomarker of severity in critically ill ARDS patients. This study explores the contribution of single nucleotide polymorphisms (SNPs) of the S1PR3 gene to sepsis-associated ARDS. S1PR3 SNPs were identified by sequencing the entire gene and tagging SNPs selected for case-control association analysis in African- and ED samples from Chicago, with independent replication in a European case-control study of Spanish individuals. Electrophoretic mobility shift assays, luciferase activity assays, and protein immunoassays were utilized to assess the functionality of associated SNPs. A total of 80 variants, including 29 novel SNPs, were identified. Because of limited sample size, conclusive findings could not be drawn in African-descent ARDS subjects; however, significant associations were found for two promoter SNPs (rs7022797 -1899T/G; rs11137480 -1785G/C), across two ED samples supporting the association of alleles -1899G and -1785C with decreased risk for sepsis-associated ARDS. In addition, these alleles significantly reduced transcription factor binding to the S1PR3 promoter; reduced S1PR3 promoter activity, a response particularly striking after TNF-α challenge; and were associated with lower plasma S1PR3 protein levels in ARDS patients. These highly functional studies support S1PR3 as a novel ARDS candidate gene and a potential target for individualized therapy.

Partial deficiency of sphingosine-1-phosphate lyase confers protection in experimental autoimmune encephalomyelitis

Background

Sphingosine-1-phosphate (S1P) regulates the egress of T cells from lymphoid organs; levels of S1P in the tissues are controlled by S1P lyase (Sgpl1). Hence, Sgpl1 offers a target to block T cell-dependent inflammatory processes. However, the involvement of Sgpl1 in models of disease has not been fully elucidated yet, since Sgpl1 KO mice have a short life-span.

Methodology

We generated inducible Sgpl1 KO mice featuring partial reduction of Sgpl1 activity and analyzed them with respect to sphingolipid levels, T-cell distribution, and response in models of inflammation.

Principal Findings

The partially Sgpl1 deficient mice are viable but feature profound reduction of peripheral T cells, similar to the constitutive KO mice. While thymic T cell development in these mice appears normal, mature T cells are retained in thymus and lymph nodes, leading to reduced T cell numbers in spleen and blood, with a skewing towards increased proportions of memory T cells and T regulatory cells. The therapeutic relevance of Sgpl1 is demonstrated by the fact that the inducible KO mice are protected in experimental autoimmune encephalomyelitis (EAE). T cell immigration into the CNS was found to be profoundly reduced. Since S1P levels in the brain of the animals are unchanged, we conclude that protection in EAE is due to the peripheral effect on T cells, leading to reduced CNS immigration, rather than on local effects in the CNS.

Significance

The data suggest Sgpl1 as a novel therapeutic target for the treatment of multiple sclerosis.

Lipopolysaccharide and sphingosine-1-phosphate cooperate to induce inflammatory molecules and leukocyte adhesion in endothelial cells

Given that TLRs and sphingosine-1-phosphate (S1P) are key players in inflammation, we explored the potential interplay between TLRs and S1P in the adhesion/inflammatory pathways in primary human endothelial cells. As determined by Western blot and flow cytometry, cells treated with LPS (a TLR4 ligand) and S1P showed significantly enhanced expression of adhesion molecules such as ICAM-1 and E-selectin compared with the effect of either ligand alone. Cell-type differences on E-selectin upregulation were observed. In contrast, no cooperation effect on ICAM-1 or E-selectin was observed with a TLR2/TLR1 ligand. Consistent with an increase in adhesion molecule expression, endothelial cell treatment with LPS plus S1P significantly enhanced adhesion of PBMCs under shear stress conditions compared with the effect of either ligand alone and exhibited comparable levels of cell adhesion strength as those after TNF-α treatment. Moreover, LPS and S1P cooperated to increase the expression of proinflammatory molecules such as IL-6, cyclooxygenase-2, and prostacyclin, as determined by ELISA and Western blot. The analysis of signaling pathways revealed the synergistic phosphorylation of ERK upon LPS plus S1P treatment of HUVEC and human aortic endothelial cells and cell-type differences on p38 and NF-κB activation. Moreover, pharmacological and small interfering RNA experiments disclosed the involvement of S1P(1/3) and NF-κB in the cooperation effect and that cell origin determines the S1P receptors and signaling routes involved. Sphingosine kinase activity induction upon LPS plus S1P treatment suggests S1P- Sphingosine kinase axis involvement. In summary, LPS and S1P cooperate to increase proinflammatory molecules in endothelial cells and, in turn, to augment leukocyte adhesion, thus exacerbating S1P-mediated proadhesive/proinflammatory properties.

Expression of sphingosine 1-phosphate receptors in the rat dorsal root ganglia and defined single isolated sensory neurons

Previously, we demonstrated that sphingosine 1-phosphate (S1P) increased the excitability of small-diameter sensory neurons, in part, through activation of S1P receptor 1 (S1PR(1)), suggesting that other S1PRs can modulate neuronal excitability. Therefore, studies were undertaken to establish the expression profiles of S1PRs in the intact dorsal root ganglion (DRG) and in defined single isolated sensory neurons. To determine mRNA expression of S1PRs in the DRG, SYBR green quantitative PCR (qPCR) was used. To determine the expression of S1PR mRNAs in single neurons of defined diameters, a preamplification protocol utilizing Taqman primer and probes was used to enhance the sensitivity of detection. The preamplification protocol also permitted detection of mRNA for two hallmark neuronal receptor/ion channels, TRPV1 and P(2)X(3). Expression profiles of S1PR mRNA isolated from lung and brain were used as positive control tissues. In the intact DRG, the order of expression of S1PRs was S1PR(3)>>R(1)≈R(2)>R(5)≈R(4). In the single neurons, the expression of S1PRs was quite variable with some neurons expressing all five subtypes, whereas some expressing only one subtype. In contrast to the DRG, S1PR(1) was the highest expressing subtype in 10 of the 18 small-, medium-, and large-diameter sensory neurons. S1PR(1) was the second highest expressor in -50% of those remaining neurons. Overall, in the single neurons, the order of expression was S1PR(1)>>R(3)≈R(5)>R(4)>R(2). The results obtained from the single defined neurons are consistent with our previous findings wherein S1PR(1) plays a prominent but not exclusive role in the enhancement of neuronal excitability.

Signaling required for blood vessel maintenance: molecular basis and pathological manifestations

As our understanding of molecular mechanisms leading to vascular formation increases, vessel maintenance including stabilization of new vessels and prevention of vessel regression began to be considered as an active process that requires specific cellular signaling. While signaling pathways such as VEGF, FGF, and angiopoietin-Tie2 are important for endothelial cell survival and junction stabilization, PDGF and TGF-β signaling modify mural cell (vascular smooth muscle cells and pericytes) functions, thus they fortify vessel integrity. Breakdown of these signaling systems results in pathological hyperpermeability and/or genetic vascular abnormalities such as vascular malformations, ultimately progressing to hemorrhage and edema. Hence, blood vessel maintenance is fundamental to controlling vascular homeostasis and tissue functions. This paper discusses signaling pathways essential for vascular maintenance and clinical conditions caused by deterioration of vessel integrity.